- : unit = ()
- : unit = ()
h : heuristic = <heuristic>
- : unit = ()
APPLY CRITERIA (Marked dependency pairs)

TRS termination of:
[1] active(U101(tt,V2)) -> mark(U102(isLNat(V2)))
[2] active(U102(tt)) -> mark(tt)
[3] active(U11(tt,N,XS)) -> mark(U12(isLNat(XS),N,XS))
[4] active(U111(tt)) -> mark(tt)
[5] active(U12(tt,N,XS)) -> mark(snd(splitAt(N,XS)))
[6] active(U121(tt)) -> mark(tt)
[7] active(U131(tt,V2)) -> mark(U132(isLNat(V2)))
[8] active(U132(tt)) -> mark(tt)
[9] active(U141(tt,V2)) -> mark(U142(isLNat(V2)))
[10] active(U142(tt)) -> mark(tt)
[11] active(U151(tt,V2)) -> mark(U152(isLNat(V2)))
[12] active(U152(tt)) -> mark(tt)
[13] active(U161(tt,N)) -> mark(cons(N,natsFrom(s(N))))
[14] active(U171(tt,N,XS)) -> mark(U172(isLNat(XS),N,XS))
[15] active(U172(tt,N,XS)) -> mark(head(afterNth(N,XS)))
[16] active(U181(tt,Y)) -> mark(U182(isLNat(Y),Y))
[17] active(U182(tt,Y)) -> mark(Y)
[18] active(U191(tt,XS)) -> mark(pair(nil,XS))
[19] active(U201(tt,N,X,XS)) -> mark(U202(isNatural(X),N,X,XS))
[20] active(U202(tt,N,X,XS)) -> mark(U203(isLNat(XS),N,X,XS))
[21] active(U203(tt,N,X,XS)) -> mark(U204(splitAt(N,XS),X))
[22] active(U204(pair(YS,ZS),X)) -> mark(pair(cons(X,YS),ZS))
[23] active(U21(tt,X,Y)) -> mark(U22(isLNat(Y),X))
[24] active(U211(tt,XS)) -> mark(U212(isLNat(XS),XS))
[25] active(U212(tt,XS)) -> mark(XS)
[26] active(U22(tt,X)) -> mark(X)
[27] active(U221(tt,N,XS)) -> mark(U222(isLNat(XS),N,XS))
[28] active(U222(tt,N,XS)) -> mark(fst(splitAt(N,XS)))
[29] active(U31(tt,N,XS)) -> mark(U32(isLNat(XS),N))
[30] active(U32(tt,N)) -> mark(N)
[31] active(U41(tt,V2)) -> mark(U42(isLNat(V2)))
[32] active(U42(tt)) -> mark(tt)
[33] active(U51(tt,V2)) -> mark(U52(isLNat(V2)))
[34] active(U52(tt)) -> mark(tt)
[35] active(U61(tt)) -> mark(tt)
[36] active(U71(tt)) -> mark(tt)
[37] active(U81(tt)) -> mark(tt)
[38] active(U91(tt)) -> mark(tt)
[39] active(afterNth(N,XS)) -> mark(U11(isNatural(N),N,XS))
[40] active(fst(pair(X,Y))) -> mark(U21(isLNat(X),X,Y))
[41] active(head(cons(N,XS))) -> mark(U31(isNatural(N),N,XS))
[42] active(isLNat(nil)) -> mark(tt)
[43] active(isLNat(afterNth(V1,V2))) -> mark(U41(isNatural(V1),V2))
[44] active(isLNat(cons(V1,V2))) -> mark(U51(isNatural(V1),V2))
[45] active(isLNat(fst(V1))) -> mark(U61(isPLNat(V1)))
[46] active(isLNat(natsFrom(V1))) -> mark(U71(isNatural(V1)))
[47] active(isLNat(snd(V1))) -> mark(U81(isPLNat(V1)))
[48] active(isLNat(tail(V1))) -> mark(U91(isLNat(V1)))
[49] active(isLNat(take(V1,V2))) -> mark(U101(isNatural(V1),V2))
[50] active(isNatural(0)) -> mark(tt)
[51] active(isNatural(head(V1))) -> mark(U111(isLNat(V1)))
[52] active(isNatural(s(V1))) -> mark(U121(isNatural(V1)))
[53] active(isNatural(sel(V1,V2))) -> mark(U131(isNatural(V1),V2))
[54] active(isPLNat(pair(V1,V2))) -> mark(U141(isLNat(V1),V2))
[55] active(isPLNat(splitAt(V1,V2))) -> mark(U151(isNatural(V1),V2))
[56] active(natsFrom(N)) -> mark(U161(isNatural(N),N))
[57] active(sel(N,XS)) -> mark(U171(isNatural(N),N,XS))
[58] active(snd(pair(X,Y))) -> mark(U181(isLNat(X),Y))
[59] active(splitAt(0,XS)) -> mark(U191(isLNat(XS),XS))
[60] active(splitAt(s(N),cons(X,XS))) -> mark(U201(isNatural(N),N,X,XS))
[61] active(tail(cons(N,XS))) -> mark(U211(isNatural(N),XS))
[62] active(take(N,XS)) -> mark(U221(isNatural(N),N,XS))
[63] mark(U101(X1,X2)) -> active(U101(mark(X1),X2))
[64] mark(tt) -> active(tt)
[65] mark(U102(X)) -> active(U102(mark(X)))
[66] mark(isLNat(X)) -> active(isLNat(X))
[67] mark(U11(X1,X2,X3)) -> active(U11(mark(X1),X2,X3))
[68] mark(U12(X1,X2,X3)) -> active(U12(mark(X1),X2,X3))
[69] mark(U111(X)) -> active(U111(mark(X)))
[70] mark(snd(X)) -> active(snd(mark(X)))
[71] mark(splitAt(X1,X2)) -> active(splitAt(mark(X1),mark(X2)))
[72] mark(U121(X)) -> active(U121(mark(X)))
[73] mark(U131(X1,X2)) -> active(U131(mark(X1),X2))
[74] mark(U132(X)) -> active(U132(mark(X)))
[75] mark(U141(X1,X2)) -> active(U141(mark(X1),X2))
[76] mark(U142(X)) -> active(U142(mark(X)))
[77] mark(U151(X1,X2)) -> active(U151(mark(X1),X2))
[78] mark(U152(X)) -> active(U152(mark(X)))
[79] mark(U161(X1,X2)) -> active(U161(mark(X1),X2))
[80] mark(cons(X1,X2)) -> active(cons(mark(X1),X2))
[81] mark(natsFrom(X)) -> active(natsFrom(mark(X)))
[82] mark(s(X)) -> active(s(mark(X)))
[83] mark(U171(X1,X2,X3)) -> active(U171(mark(X1),X2,X3))
[84] mark(U172(X1,X2,X3)) -> active(U172(mark(X1),X2,X3))
[85] mark(head(X)) -> active(head(mark(X)))
[86] mark(afterNth(X1,X2)) -> active(afterNth(mark(X1),mark(X2)))
[87] mark(U181(X1,X2)) -> active(U181(mark(X1),X2))
[88] mark(U182(X1,X2)) -> active(U182(mark(X1),X2))
[89] mark(U191(X1,X2)) -> active(U191(mark(X1),X2))
[90] mark(pair(X1,X2)) -> active(pair(mark(X1),mark(X2)))
[91] mark(nil) -> active(nil)
[92] mark(U201(X1,X2,X3,X4)) -> active(U201(mark(X1),X2,X3,X4))
[93] mark(U202(X1,X2,X3,X4)) -> active(U202(mark(X1),X2,X3,X4))
[94] mark(isNatural(X)) -> active(isNatural(X))
[95] mark(U203(X1,X2,X3,X4)) -> active(U203(mark(X1),X2,X3,X4))
[96] mark(U204(X1,X2)) -> active(U204(mark(X1),X2))
[97] mark(U21(X1,X2,X3)) -> active(U21(mark(X1),X2,X3))
[98] mark(U22(X1,X2)) -> active(U22(mark(X1),X2))
[99] mark(U211(X1,X2)) -> active(U211(mark(X1),X2))
[100] mark(U212(X1,X2)) -> active(U212(mark(X1),X2))
[101] mark(U221(X1,X2,X3)) -> active(U221(mark(X1),X2,X3))
[102] mark(U222(X1,X2,X3)) -> active(U222(mark(X1),X2,X3))
[103] mark(fst(X)) -> active(fst(mark(X)))
[104] mark(U31(X1,X2,X3)) -> active(U31(mark(X1),X2,X3))
[105] mark(U32(X1,X2)) -> active(U32(mark(X1),X2))
[106] mark(U41(X1,X2)) -> active(U41(mark(X1),X2))
[107] mark(U42(X)) -> active(U42(mark(X)))
[108] mark(U51(X1,X2)) -> active(U51(mark(X1),X2))
[109] mark(U52(X)) -> active(U52(mark(X)))
[110] mark(U61(X)) -> active(U61(mark(X)))
[111] mark(U71(X)) -> active(U71(mark(X)))
[112] mark(U81(X)) -> active(U81(mark(X)))
[113] mark(U91(X)) -> active(U91(mark(X)))
[114] mark(isPLNat(X)) -> active(isPLNat(X))
[115] mark(tail(X)) -> active(tail(mark(X)))
[116] mark(take(X1,X2)) -> active(take(mark(X1),mark(X2)))
[117] mark(0) -> active(0)
[118] mark(sel(X1,X2)) -> active(sel(mark(X1),mark(X2)))
[119] U101(mark(X1),X2) -> U101(X1,X2)
[120] U101(X1,mark(X2)) -> U101(X1,X2)
[121] U101(active(X1),X2) -> U101(X1,X2)
[122] U101(X1,active(X2)) -> U101(X1,X2)
[123] U102(mark(X)) -> U102(X)
[124] U102(active(X)) -> U102(X)
[125] isLNat(mark(X)) -> isLNat(X)
[126] isLNat(active(X)) -> isLNat(X)
[127] U11(mark(X1),X2,X3) -> U11(X1,X2,X3)
[128] U11(X1,mark(X2),X3) -> U11(X1,X2,X3)
[129] U11(X1,X2,mark(X3)) -> U11(X1,X2,X3)
[130] U11(active(X1),X2,X3) -> U11(X1,X2,X3)
[131] U11(X1,active(X2),X3) -> U11(X1,X2,X3)
[132] U11(X1,X2,active(X3)) -> U11(X1,X2,X3)
[133] U12(mark(X1),X2,X3) -> U12(X1,X2,X3)
[134] U12(X1,mark(X2),X3) -> U12(X1,X2,X3)
[135] U12(X1,X2,mark(X3)) -> U12(X1,X2,X3)
[136] U12(active(X1),X2,X3) -> U12(X1,X2,X3)
[137] U12(X1,active(X2),X3) -> U12(X1,X2,X3)
[138] U12(X1,X2,active(X3)) -> U12(X1,X2,X3)
[139] U111(mark(X)) -> U111(X)
[140] U111(active(X)) -> U111(X)
[141] snd(mark(X)) -> snd(X)
[142] snd(active(X)) -> snd(X)
[143] splitAt(mark(X1),X2) -> splitAt(X1,X2)
[144] splitAt(X1,mark(X2)) -> splitAt(X1,X2)
[145] splitAt(active(X1),X2) -> splitAt(X1,X2)
[146] splitAt(X1,active(X2)) -> splitAt(X1,X2)
[147] U121(mark(X)) -> U121(X)
[148] U121(active(X)) -> U121(X)
[149] U131(mark(X1),X2) -> U131(X1,X2)
[150] U131(X1,mark(X2)) -> U131(X1,X2)
[151] U131(active(X1),X2) -> U131(X1,X2)
[152] U131(X1,active(X2)) -> U131(X1,X2)
[153] U132(mark(X)) -> U132(X)
[154] U132(active(X)) -> U132(X)
[155] U141(mark(X1),X2) -> U141(X1,X2)
[156] U141(X1,mark(X2)) -> U141(X1,X2)
[157] U141(active(X1),X2) -> U141(X1,X2)
[158] U141(X1,active(X2)) -> U141(X1,X2)
[159] U142(mark(X)) -> U142(X)
[160] U142(active(X)) -> U142(X)
[161] U151(mark(X1),X2) -> U151(X1,X2)
[162] U151(X1,mark(X2)) -> U151(X1,X2)
[163] U151(active(X1),X2) -> U151(X1,X2)
[164] U151(X1,active(X2)) -> U151(X1,X2)
[165] U152(mark(X)) -> U152(X)
[166] U152(active(X)) -> U152(X)
[167] U161(mark(X1),X2) -> U161(X1,X2)
[168] U161(X1,mark(X2)) -> U161(X1,X2)
[169] U161(active(X1),X2) -> U161(X1,X2)
[170] U161(X1,active(X2)) -> U161(X1,X2)
[171] cons(mark(X1),X2) -> cons(X1,X2)
[172] cons(X1,mark(X2)) -> cons(X1,X2)
[173] cons(active(X1),X2) -> cons(X1,X2)
[174] cons(X1,active(X2)) -> cons(X1,X2)
[175] natsFrom(mark(X)) -> natsFrom(X)
[176] natsFrom(active(X)) -> natsFrom(X)
[177] s(mark(X)) -> s(X)
[178] s(active(X)) -> s(X)
[179] U171(mark(X1),X2,X3) -> U171(X1,X2,X3)
[180] U171(X1,mark(X2),X3) -> U171(X1,X2,X3)
[181] U171(X1,X2,mark(X3)) -> U171(X1,X2,X3)
[182] U171(active(X1),X2,X3) -> U171(X1,X2,X3)
[183] U171(X1,active(X2),X3) -> U171(X1,X2,X3)
[184] U171(X1,X2,active(X3)) -> U171(X1,X2,X3)
[185] U172(mark(X1),X2,X3) -> U172(X1,X2,X3)
[186] U172(X1,mark(X2),X3) -> U172(X1,X2,X3)
[187] U172(X1,X2,mark(X3)) -> U172(X1,X2,X3)
[188] U172(active(X1),X2,X3) -> U172(X1,X2,X3)
[189] U172(X1,active(X2),X3) -> U172(X1,X2,X3)
[190] U172(X1,X2,active(X3)) -> U172(X1,X2,X3)
[191] head(mark(X)) -> head(X)
[192] head(active(X)) -> head(X)
[193] afterNth(mark(X1),X2) -> afterNth(X1,X2)
[194] afterNth(X1,mark(X2)) -> afterNth(X1,X2)
[195] afterNth(active(X1),X2) -> afterNth(X1,X2)
[196] afterNth(X1,active(X2)) -> afterNth(X1,X2)
[197] U181(mark(X1),X2) -> U181(X1,X2)
[198] U181(X1,mark(X2)) -> U181(X1,X2)
[199] U181(active(X1),X2) -> U181(X1,X2)
[200] U181(X1,active(X2)) -> U181(X1,X2)
[201] U182(mark(X1),X2) -> U182(X1,X2)
[202] U182(X1,mark(X2)) -> U182(X1,X2)
[203] U182(active(X1),X2) -> U182(X1,X2)
[204] U182(X1,active(X2)) -> U182(X1,X2)
[205] U191(mark(X1),X2) -> U191(X1,X2)
[206] U191(X1,mark(X2)) -> U191(X1,X2)
[207] U191(active(X1),X2) -> U191(X1,X2)
[208] U191(X1,active(X2)) -> U191(X1,X2)
[209] pair(mark(X1),X2) -> pair(X1,X2)
[210] pair(X1,mark(X2)) -> pair(X1,X2)
[211] pair(active(X1),X2) -> pair(X1,X2)
[212] pair(X1,active(X2)) -> pair(X1,X2)
[213] U201(mark(X1),X2,X3,X4) -> U201(X1,X2,X3,X4)
[214] U201(X1,mark(X2),X3,X4) -> U201(X1,X2,X3,X4)
[215] U201(X1,X2,mark(X3),X4) -> U201(X1,X2,X3,X4)
[216] U201(X1,X2,X3,mark(X4)) -> U201(X1,X2,X3,X4)
[217] U201(active(X1),X2,X3,X4) -> U201(X1,X2,X3,X4)
[218] U201(X1,active(X2),X3,X4) -> U201(X1,X2,X3,X4)
[219] U201(X1,X2,active(X3),X4) -> U201(X1,X2,X3,X4)
[220] U201(X1,X2,X3,active(X4)) -> U201(X1,X2,X3,X4)
[221] U202(mark(X1),X2,X3,X4) -> U202(X1,X2,X3,X4)
[222] U202(X1,mark(X2),X3,X4) -> U202(X1,X2,X3,X4)
[223] U202(X1,X2,mark(X3),X4) -> U202(X1,X2,X3,X4)
[224] U202(X1,X2,X3,mark(X4)) -> U202(X1,X2,X3,X4)
[225] U202(active(X1),X2,X3,X4) -> U202(X1,X2,X3,X4)
[226] U202(X1,active(X2),X3,X4) -> U202(X1,X2,X3,X4)
[227] U202(X1,X2,active(X3),X4) -> U202(X1,X2,X3,X4)
[228] U202(X1,X2,X3,active(X4)) -> U202(X1,X2,X3,X4)
[229] isNatural(mark(X)) -> isNatural(X)
[230] isNatural(active(X)) -> isNatural(X)
[231] U203(mark(X1),X2,X3,X4) -> U203(X1,X2,X3,X4)
[232] U203(X1,mark(X2),X3,X4) -> U203(X1,X2,X3,X4)
[233] U203(X1,X2,mark(X3),X4) -> U203(X1,X2,X3,X4)
[234] U203(X1,X2,X3,mark(X4)) -> U203(X1,X2,X3,X4)
[235] U203(active(X1),X2,X3,X4) -> U203(X1,X2,X3,X4)
[236] U203(X1,active(X2),X3,X4) -> U203(X1,X2,X3,X4)
[237] U203(X1,X2,active(X3),X4) -> U203(X1,X2,X3,X4)
[238] U203(X1,X2,X3,active(X4)) -> U203(X1,X2,X3,X4)
[239] U204(mark(X1),X2) -> U204(X1,X2)
[240] U204(X1,mark(X2)) -> U204(X1,X2)
[241] U204(active(X1),X2) -> U204(X1,X2)
[242] U204(X1,active(X2)) -> U204(X1,X2)
[243] U21(mark(X1),X2,X3) -> U21(X1,X2,X3)
[244] U21(X1,mark(X2),X3) -> U21(X1,X2,X3)
[245] U21(X1,X2,mark(X3)) -> U21(X1,X2,X3)
[246] U21(active(X1),X2,X3) -> U21(X1,X2,X3)
[247] U21(X1,active(X2),X3) -> U21(X1,X2,X3)
[248] U21(X1,X2,active(X3)) -> U21(X1,X2,X3)
[249] U22(mark(X1),X2) -> U22(X1,X2)
[250] U22(X1,mark(X2)) -> U22(X1,X2)
[251] U22(active(X1),X2) -> U22(X1,X2)
[252] U22(X1,active(X2)) -> U22(X1,X2)
[253] U211(mark(X1),X2) -> U211(X1,X2)
[254] U211(X1,mark(X2)) -> U211(X1,X2)
[255] U211(active(X1),X2) -> U211(X1,X2)
[256] U211(X1,active(X2)) -> U211(X1,X2)
[257] U212(mark(X1),X2) -> U212(X1,X2)
[258] U212(X1,mark(X2)) -> U212(X1,X2)
[259] U212(active(X1),X2) -> U212(X1,X2)
[260] U212(X1,active(X2)) -> U212(X1,X2)
[261] U221(mark(X1),X2,X3) -> U221(X1,X2,X3)
[262] U221(X1,mark(X2),X3) -> U221(X1,X2,X3)
[263] U221(X1,X2,mark(X3)) -> U221(X1,X2,X3)
[264] U221(active(X1),X2,X3) -> U221(X1,X2,X3)
[265] U221(X1,active(X2),X3) -> U221(X1,X2,X3)
[266] U221(X1,X2,active(X3)) -> U221(X1,X2,X3)
[267] U222(mark(X1),X2,X3) -> U222(X1,X2,X3)
[268] U222(X1,mark(X2),X3) -> U222(X1,X2,X3)
[269] U222(X1,X2,mark(X3)) -> U222(X1,X2,X3)
[270] U222(active(X1),X2,X3) -> U222(X1,X2,X3)
[271] U222(X1,active(X2),X3) -> U222(X1,X2,X3)
[272] U222(X1,X2,active(X3)) -> U222(X1,X2,X3)
[273] fst(mark(X)) -> fst(X)
[274] fst(active(X)) -> fst(X)
[275] U31(mark(X1),X2,X3) -> U31(X1,X2,X3)
[276] U31(X1,mark(X2),X3) -> U31(X1,X2,X3)
[277] U31(X1,X2,mark(X3)) -> U31(X1,X2,X3)
[278] U31(active(X1),X2,X3) -> U31(X1,X2,X3)
[279] U31(X1,active(X2),X3) -> U31(X1,X2,X3)
[280] U31(X1,X2,active(X3)) -> U31(X1,X2,X3)
[281] U32(mark(X1),X2) -> U32(X1,X2)
[282] U32(X1,mark(X2)) -> U32(X1,X2)
[283] U32(active(X1),X2) -> U32(X1,X2)
[284] U32(X1,active(X2)) -> U32(X1,X2)
[285] U41(mark(X1),X2) -> U41(X1,X2)
[286] U41(X1,mark(X2)) -> U41(X1,X2)
[287] U41(active(X1),X2) -> U41(X1,X2)
[288] U41(X1,active(X2)) -> U41(X1,X2)
[289] U42(mark(X)) -> U42(X)
[290] U42(active(X)) -> U42(X)
[291] U51(mark(X1),X2) -> U51(X1,X2)
[292] U51(X1,mark(X2)) -> U51(X1,X2)
[293] U51(active(X1),X2) -> U51(X1,X2)
[294] U51(X1,active(X2)) -> U51(X1,X2)
[295] U52(mark(X)) -> U52(X)
[296] U52(active(X)) -> U52(X)
[297] U61(mark(X)) -> U61(X)
[298] U61(active(X)) -> U61(X)
[299] U71(mark(X)) -> U71(X)
[300] U71(active(X)) -> U71(X)
[301] U81(mark(X)) -> U81(X)
[302] U81(active(X)) -> U81(X)
[303] U91(mark(X)) -> U91(X)
[304] U91(active(X)) -> U91(X)
[305] isPLNat(mark(X)) -> isPLNat(X)
[306] isPLNat(active(X)) -> isPLNat(X)
[307] tail(mark(X)) -> tail(X)
[308] tail(active(X)) -> tail(X)
[309] take(mark(X1),X2) -> take(X1,X2)
[310] take(X1,mark(X2)) -> take(X1,X2)
[311] take(active(X1),X2) -> take(X1,X2)
[312] take(X1,active(X2)) -> take(X1,X2)
[313] sel(mark(X1),X2) -> sel(X1,X2)
[314] sel(X1,mark(X2)) -> sel(X1,X2)
[315] sel(active(X1),X2) -> sel(X1,X2)
[316] sel(X1,active(X2)) -> sel(X1,X2)


Sub problem: 
guided: 

DP termination of:
<Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
<Marked_active(U101(tt,V2)) , Marked_U102(isLNat(V2))>
<Marked_active(U101(tt,V2)) , Marked_isLNat(V2)>
<Marked_active(U102(tt)) , Marked_mark(tt)>
<Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
<Marked_active(U11(tt,N,XS)) , Marked_U12(isLNat(XS),N,XS)>
<Marked_active(U11(tt,N,XS)) , Marked_isLNat(XS)>
<Marked_active(U111(tt)) , Marked_mark(tt)>
<Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
<Marked_active(U12(tt,N,XS)) , Marked_snd(splitAt(N,XS))>
<Marked_active(U12(tt,N,XS)) , Marked_splitAt(N,XS)>
<Marked_active(U121(tt)) , Marked_mark(tt)>
<Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
<Marked_active(U131(tt,V2)) , Marked_U132(isLNat(V2))>
<Marked_active(U131(tt,V2)) , Marked_isLNat(V2)>
<Marked_active(U132(tt)) , Marked_mark(tt)>
<Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
<Marked_active(U141(tt,V2)) , Marked_U142(isLNat(V2))>
<Marked_active(U141(tt,V2)) , Marked_isLNat(V2)>
<Marked_active(U142(tt)) , Marked_mark(tt)>
<Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
<Marked_active(U151(tt,V2)) , Marked_U152(isLNat(V2))>
<Marked_active(U151(tt,V2)) , Marked_isLNat(V2)>
<Marked_active(U152(tt)) , Marked_mark(tt)>
<Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
<Marked_active(U161(tt,N)) , Marked_cons(N,natsFrom(s(N)))>
<Marked_active(U161(tt,N)) , Marked_natsFrom(s(N))>
<Marked_active(U161(tt,N)) , Marked_s(N)>
<Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
<Marked_active(U171(tt,N,XS)) , Marked_U172(isLNat(XS),N,XS)>
<Marked_active(U171(tt,N,XS)) , Marked_isLNat(XS)>
<Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
<Marked_active(U172(tt,N,XS)) , Marked_head(afterNth(N,XS))>
<Marked_active(U172(tt,N,XS)) , Marked_afterNth(N,XS)>
<Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
<Marked_active(U181(tt,Y)) , Marked_U182(isLNat(Y),Y)>
<Marked_active(U181(tt,Y)) , Marked_isLNat(Y)>
<Marked_active(U182(tt,Y)) , Marked_mark(Y)>
<Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
<Marked_active(U191(tt,XS)) , Marked_pair(nil,XS)>
<Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),N,X,XS))>
<Marked_active(U201(tt,N,X,XS)) , Marked_U202(isNatural(X),N,X,XS)>
<Marked_active(U201(tt,N,X,XS)) , Marked_isNatural(X)>
<Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
<Marked_active(U202(tt,N,X,XS)) , Marked_U203(isLNat(XS),N,X,XS)>
<Marked_active(U202(tt,N,X,XS)) , Marked_isLNat(XS)>
<Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
<Marked_active(U203(tt,N,X,XS)) , Marked_U204(splitAt(N,XS),X)>
<Marked_active(U203(tt,N,X,XS)) , Marked_splitAt(N,XS)>
<Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
<Marked_active(U204(pair(YS,ZS),X)) , Marked_pair(cons(X,YS),ZS)>
<Marked_active(U204(pair(YS,ZS),X)) , Marked_cons(X,YS)>
<Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
<Marked_active(U21(tt,X,Y)) , Marked_U22(isLNat(Y),X)>
<Marked_active(U21(tt,X,Y)) , Marked_isLNat(Y)>
<Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
<Marked_active(U211(tt,XS)) , Marked_U212(isLNat(XS),XS)>
<Marked_active(U211(tt,XS)) , Marked_isLNat(XS)>
<Marked_active(U212(tt,XS)) , Marked_mark(XS)>
<Marked_active(U22(tt,X)) , Marked_mark(X)>
<Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
<Marked_active(U221(tt,N,XS)) , Marked_U222(isLNat(XS),N,XS)>
<Marked_active(U221(tt,N,XS)) , Marked_isLNat(XS)>
<Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
<Marked_active(U222(tt,N,XS)) , Marked_fst(splitAt(N,XS))>
<Marked_active(U222(tt,N,XS)) , Marked_splitAt(N,XS)>
<Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
<Marked_active(U31(tt,N,XS)) , Marked_U32(isLNat(XS),N)>
<Marked_active(U31(tt,N,XS)) , Marked_isLNat(XS)>
<Marked_active(U32(tt,N)) , Marked_mark(N)>
<Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
<Marked_active(U41(tt,V2)) , Marked_U42(isLNat(V2))>
<Marked_active(U41(tt,V2)) , Marked_isLNat(V2)>
<Marked_active(U42(tt)) , Marked_mark(tt)>
<Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
<Marked_active(U51(tt,V2)) , Marked_U52(isLNat(V2))>
<Marked_active(U51(tt,V2)) , Marked_isLNat(V2)>
<Marked_active(U52(tt)) , Marked_mark(tt)>
<Marked_active(U61(tt)) , Marked_mark(tt)>
<Marked_active(U71(tt)) , Marked_mark(tt)>
<Marked_active(U81(tt)) , Marked_mark(tt)>
<Marked_active(U91(tt)) , Marked_mark(tt)>
<Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
<Marked_active(afterNth(N,XS)) , Marked_U11(isNatural(N),N,XS)>
<Marked_active(afterNth(N,XS)) , Marked_isNatural(N)>
<Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
<Marked_active(fst(pair(X,Y))) , Marked_U21(isLNat(X),X,Y)>
<Marked_active(fst(pair(X,Y))) , Marked_isLNat(X)>
<Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
<Marked_active(head(cons(N,XS))) , Marked_U31(isNatural(N),N,XS)>
<Marked_active(head(cons(N,XS))) , Marked_isNatural(N)>
<Marked_active(isLNat(nil)) , Marked_mark(tt)>
<Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(V1),V2))>
<Marked_active(isLNat(afterNth(V1,V2))) , Marked_U41(isNatural(V1),V2)>
<Marked_active(isLNat(afterNth(V1,V2))) , Marked_isNatural(V1)>
<Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),V2))>
<Marked_active(isLNat(cons(V1,V2))) , Marked_U51(isNatural(V1),V2)>
<Marked_active(isLNat(cons(V1,V2))) , Marked_isNatural(V1)>
<Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
<Marked_active(isLNat(fst(V1))) , Marked_U61(isPLNat(V1))>
<Marked_active(isLNat(fst(V1))) , Marked_isPLNat(V1)>
<Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
<Marked_active(isLNat(natsFrom(V1))) , Marked_U71(isNatural(V1))>
<Marked_active(isLNat(natsFrom(V1))) , Marked_isNatural(V1)>
<Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
<Marked_active(isLNat(snd(V1))) , Marked_U81(isPLNat(V1))>
<Marked_active(isLNat(snd(V1))) , Marked_isPLNat(V1)>
<Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
<Marked_active(isLNat(tail(V1))) , Marked_U91(isLNat(V1))>
<Marked_active(isLNat(tail(V1))) , Marked_isLNat(V1)>
<Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),V2))>
<Marked_active(isLNat(take(V1,V2))) , Marked_U101(isNatural(V1),V2)>
<Marked_active(isLNat(take(V1,V2))) , Marked_isNatural(V1)>
<Marked_active(isNatural(0)) , Marked_mark(tt)>
<Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
<Marked_active(isNatural(head(V1))) , Marked_U111(isLNat(V1))>
<Marked_active(isNatural(head(V1))) , Marked_isLNat(V1)>
<Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
<Marked_active(isNatural(s(V1))) , Marked_U121(isNatural(V1))>
<Marked_active(isNatural(s(V1))) , Marked_isNatural(V1)>
<Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),V2))>
<Marked_active(isNatural(sel(V1,V2))) , Marked_U131(isNatural(V1),V2)>
<Marked_active(isNatural(sel(V1,V2))) , Marked_isNatural(V1)>
<Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
<Marked_active(isPLNat(pair(V1,V2))) , Marked_U141(isLNat(V1),V2)>
<Marked_active(isPLNat(pair(V1,V2))) , Marked_isLNat(V1)>
<Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(V1),V2))>
<Marked_active(isPLNat(splitAt(V1,V2))) , Marked_U151(isNatural(V1),V2)>
<Marked_active(isPLNat(splitAt(V1,V2))) , Marked_isNatural(V1)>
<Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
<Marked_active(natsFrom(N)) , Marked_U161(isNatural(N),N)>
<Marked_active(natsFrom(N)) , Marked_isNatural(N)>
<Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
<Marked_active(sel(N,XS)) , Marked_U171(isNatural(N),N,XS)>
<Marked_active(sel(N,XS)) , Marked_isNatural(N)>
<Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
<Marked_active(snd(pair(X,Y))) , Marked_U181(isLNat(X),Y)>
<Marked_active(snd(pair(X,Y))) , Marked_isLNat(X)>
<Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
<Marked_active(splitAt(0,XS)) , Marked_U191(isLNat(XS),XS)>
<Marked_active(splitAt(0,XS)) , Marked_isLNat(XS)>
<Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(isNatural(N),
                                                        N,X,XS))>
<Marked_active(splitAt(s(N),cons(X,XS))) , Marked_U201(isNatural(N),N,X,XS)>
<Marked_active(splitAt(s(N),cons(X,XS))) , Marked_isNatural(N)>
<Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
<Marked_active(tail(cons(N,XS))) , Marked_U211(isNatural(N),XS)>
<Marked_active(tail(cons(N,XS))) , Marked_isNatural(N)>
<Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
<Marked_active(take(N,XS)) , Marked_U221(isNatural(N),N,XS)>
<Marked_active(take(N,XS)) , Marked_isNatural(N)>
<Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
<Marked_mark(U101(X1,X2)) , Marked_U101(mark(X1),X2)>
<Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
<Marked_mark(tt) , Marked_active(tt)>
<Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
<Marked_mark(U102(X)) , Marked_U102(mark(X))>
<Marked_mark(U102(X)) , Marked_mark(X)>
<Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
<Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
<Marked_mark(U11(X1,X2,X3)) , Marked_U11(mark(X1),X2,X3)>
<Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
<Marked_mark(U12(X1,X2,X3)) , Marked_U12(mark(X1),X2,X3)>
<Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
<Marked_mark(U111(X)) , Marked_U111(mark(X))>
<Marked_mark(U111(X)) , Marked_mark(X)>
<Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
<Marked_mark(snd(X)) , Marked_snd(mark(X))>
<Marked_mark(snd(X)) , Marked_mark(X)>
<Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))>
<Marked_mark(splitAt(X1,X2)) , Marked_splitAt(mark(X1),mark(X2))>
<Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
<Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
<Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
<Marked_mark(U121(X)) , Marked_U121(mark(X))>
<Marked_mark(U121(X)) , Marked_mark(X)>
<Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
<Marked_mark(U131(X1,X2)) , Marked_U131(mark(X1),X2)>
<Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
<Marked_mark(U132(X)) , Marked_U132(mark(X))>
<Marked_mark(U132(X)) , Marked_mark(X)>
<Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
<Marked_mark(U141(X1,X2)) , Marked_U141(mark(X1),X2)>
<Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
<Marked_mark(U142(X)) , Marked_U142(mark(X))>
<Marked_mark(U142(X)) , Marked_mark(X)>
<Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
<Marked_mark(U151(X1,X2)) , Marked_U151(mark(X1),X2)>
<Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
<Marked_mark(U152(X)) , Marked_U152(mark(X))>
<Marked_mark(U152(X)) , Marked_mark(X)>
<Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
<Marked_mark(U161(X1,X2)) , Marked_U161(mark(X1),X2)>
<Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
<Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
<Marked_mark(cons(X1,X2)) , Marked_cons(mark(X1),X2)>
<Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
<Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
<Marked_mark(natsFrom(X)) , Marked_natsFrom(mark(X))>
<Marked_mark(natsFrom(X)) , Marked_mark(X)>
<Marked_mark(s(X)) , Marked_active(s(mark(X)))>
<Marked_mark(s(X)) , Marked_s(mark(X))>
<Marked_mark(s(X)) , Marked_mark(X)>
<Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
<Marked_mark(U171(X1,X2,X3)) , Marked_U171(mark(X1),X2,X3)>
<Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
<Marked_mark(U172(X1,X2,X3)) , Marked_U172(mark(X1),X2,X3)>
<Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(head(X)) , Marked_active(head(mark(X)))>
<Marked_mark(head(X)) , Marked_head(mark(X))>
<Marked_mark(head(X)) , Marked_mark(X)>
<Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))>
<Marked_mark(afterNth(X1,X2)) , Marked_afterNth(mark(X1),mark(X2))>
<Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
<Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
<Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
<Marked_mark(U181(X1,X2)) , Marked_U181(mark(X1),X2)>
<Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
<Marked_mark(U182(X1,X2)) , Marked_U182(mark(X1),X2)>
<Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
<Marked_mark(U191(X1,X2)) , Marked_U191(mark(X1),X2)>
<Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
<Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
<Marked_mark(pair(X1,X2)) , Marked_pair(mark(X1),mark(X2))>
<Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
<Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
<Marked_mark(nil) , Marked_active(nil)>
<Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))>
<Marked_mark(U201(X1,X2,X3,X4)) , Marked_U201(mark(X1),X2,X3,X4)>
<Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
<Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))>
<Marked_mark(U202(X1,X2,X3,X4)) , Marked_U202(mark(X1),X2,X3,X4)>
<Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
<Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
<Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))>
<Marked_mark(U203(X1,X2,X3,X4)) , Marked_U203(mark(X1),X2,X3,X4)>
<Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
<Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
<Marked_mark(U204(X1,X2)) , Marked_U204(mark(X1),X2)>
<Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
<Marked_mark(U21(X1,X2,X3)) , Marked_U21(mark(X1),X2,X3)>
<Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
<Marked_mark(U22(X1,X2)) , Marked_U22(mark(X1),X2)>
<Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
<Marked_mark(U211(X1,X2)) , Marked_U211(mark(X1),X2)>
<Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
<Marked_mark(U212(X1,X2)) , Marked_U212(mark(X1),X2)>
<Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
<Marked_mark(U221(X1,X2,X3)) , Marked_U221(mark(X1),X2,X3)>
<Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
<Marked_mark(U222(X1,X2,X3)) , Marked_U222(mark(X1),X2,X3)>
<Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
<Marked_mark(fst(X)) , Marked_fst(mark(X))>
<Marked_mark(fst(X)) , Marked_mark(X)>
<Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
<Marked_mark(U31(X1,X2,X3)) , Marked_U31(mark(X1),X2,X3)>
<Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
<Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
<Marked_mark(U32(X1,X2)) , Marked_U32(mark(X1),X2)>
<Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
<Marked_mark(U41(X1,X2)) , Marked_U41(mark(X1),X2)>
<Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
<Marked_mark(U42(X)) , Marked_U42(mark(X))>
<Marked_mark(U42(X)) , Marked_mark(X)>
<Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
<Marked_mark(U51(X1,X2)) , Marked_U51(mark(X1),X2)>
<Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
<Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
<Marked_mark(U52(X)) , Marked_U52(mark(X))>
<Marked_mark(U52(X)) , Marked_mark(X)>
<Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
<Marked_mark(U61(X)) , Marked_U61(mark(X))>
<Marked_mark(U61(X)) , Marked_mark(X)>
<Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
<Marked_mark(U71(X)) , Marked_U71(mark(X))>
<Marked_mark(U71(X)) , Marked_mark(X)>
<Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
<Marked_mark(U81(X)) , Marked_U81(mark(X))>
<Marked_mark(U81(X)) , Marked_mark(X)>
<Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
<Marked_mark(U91(X)) , Marked_U91(mark(X))>
<Marked_mark(U91(X)) , Marked_mark(X)>
<Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
<Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
<Marked_mark(tail(X)) , Marked_tail(mark(X))>
<Marked_mark(tail(X)) , Marked_mark(X)>
<Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
<Marked_mark(take(X1,X2)) , Marked_take(mark(X1),mark(X2))>
<Marked_mark(take(X1,X2)) , Marked_mark(X1)>
<Marked_mark(take(X1,X2)) , Marked_mark(X2)>
<Marked_mark(0) , Marked_active(0)>
<Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
<Marked_mark(sel(X1,X2)) , Marked_sel(mark(X1),mark(X2))>
<Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
<Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
<Marked_U101(mark(X1),X2) , Marked_U101(X1,X2)>
<Marked_U101(X1,mark(X2)) , Marked_U101(X1,X2)>
<Marked_U101(active(X1),X2) , Marked_U101(X1,X2)>
<Marked_U101(X1,active(X2)) , Marked_U101(X1,X2)>
<Marked_U102(mark(X)) , Marked_U102(X)>
<Marked_U102(active(X)) , Marked_U102(X)>
<Marked_isLNat(mark(X)) , Marked_isLNat(X)>
<Marked_isLNat(active(X)) , Marked_isLNat(X)>
<Marked_U11(mark(X1),X2,X3) , Marked_U11(X1,X2,X3)>
<Marked_U11(X1,mark(X2),X3) , Marked_U11(X1,X2,X3)>
<Marked_U11(X1,X2,mark(X3)) , Marked_U11(X1,X2,X3)>
<Marked_U11(active(X1),X2,X3) , Marked_U11(X1,X2,X3)>
<Marked_U11(X1,active(X2),X3) , Marked_U11(X1,X2,X3)>
<Marked_U11(X1,X2,active(X3)) , Marked_U11(X1,X2,X3)>
<Marked_U12(mark(X1),X2,X3) , Marked_U12(X1,X2,X3)>
<Marked_U12(X1,mark(X2),X3) , Marked_U12(X1,X2,X3)>
<Marked_U12(X1,X2,mark(X3)) , Marked_U12(X1,X2,X3)>
<Marked_U12(active(X1),X2,X3) , Marked_U12(X1,X2,X3)>
<Marked_U12(X1,active(X2),X3) , Marked_U12(X1,X2,X3)>
<Marked_U12(X1,X2,active(X3)) , Marked_U12(X1,X2,X3)>
<Marked_U111(mark(X)) , Marked_U111(X)>
<Marked_U111(active(X)) , Marked_U111(X)>
<Marked_snd(mark(X)) , Marked_snd(X)>
<Marked_snd(active(X)) , Marked_snd(X)>
<Marked_splitAt(mark(X1),X2) , Marked_splitAt(X1,X2)>
<Marked_splitAt(X1,mark(X2)) , Marked_splitAt(X1,X2)>
<Marked_splitAt(active(X1),X2) , Marked_splitAt(X1,X2)>
<Marked_splitAt(X1,active(X2)) , Marked_splitAt(X1,X2)>
<Marked_U121(mark(X)) , Marked_U121(X)>
<Marked_U121(active(X)) , Marked_U121(X)>
<Marked_U131(mark(X1),X2) , Marked_U131(X1,X2)>
<Marked_U131(X1,mark(X2)) , Marked_U131(X1,X2)>
<Marked_U131(active(X1),X2) , Marked_U131(X1,X2)>
<Marked_U131(X1,active(X2)) , Marked_U131(X1,X2)>
<Marked_U132(mark(X)) , Marked_U132(X)>
<Marked_U132(active(X)) , Marked_U132(X)>
<Marked_U141(mark(X1),X2) , Marked_U141(X1,X2)>
<Marked_U141(X1,mark(X2)) , Marked_U141(X1,X2)>
<Marked_U141(active(X1),X2) , Marked_U141(X1,X2)>
<Marked_U141(X1,active(X2)) , Marked_U141(X1,X2)>
<Marked_U142(mark(X)) , Marked_U142(X)>
<Marked_U142(active(X)) , Marked_U142(X)>
<Marked_U151(mark(X1),X2) , Marked_U151(X1,X2)>
<Marked_U151(X1,mark(X2)) , Marked_U151(X1,X2)>
<Marked_U151(active(X1),X2) , Marked_U151(X1,X2)>
<Marked_U151(X1,active(X2)) , Marked_U151(X1,X2)>
<Marked_U152(mark(X)) , Marked_U152(X)>
<Marked_U152(active(X)) , Marked_U152(X)>
<Marked_U161(mark(X1),X2) , Marked_U161(X1,X2)>
<Marked_U161(X1,mark(X2)) , Marked_U161(X1,X2)>
<Marked_U161(active(X1),X2) , Marked_U161(X1,X2)>
<Marked_U161(X1,active(X2)) , Marked_U161(X1,X2)>
<Marked_cons(mark(X1),X2) , Marked_cons(X1,X2)>
<Marked_cons(X1,mark(X2)) , Marked_cons(X1,X2)>
<Marked_cons(active(X1),X2) , Marked_cons(X1,X2)>
<Marked_cons(X1,active(X2)) , Marked_cons(X1,X2)>
<Marked_natsFrom(mark(X)) , Marked_natsFrom(X)>
<Marked_natsFrom(active(X)) , Marked_natsFrom(X)>
<Marked_s(mark(X)) , Marked_s(X)>
<Marked_s(active(X)) , Marked_s(X)>
<Marked_U171(mark(X1),X2,X3) , Marked_U171(X1,X2,X3)>
<Marked_U171(X1,mark(X2),X3) , Marked_U171(X1,X2,X3)>
<Marked_U171(X1,X2,mark(X3)) , Marked_U171(X1,X2,X3)>
<Marked_U171(active(X1),X2,X3) , Marked_U171(X1,X2,X3)>
<Marked_U171(X1,active(X2),X3) , Marked_U171(X1,X2,X3)>
<Marked_U171(X1,X2,active(X3)) , Marked_U171(X1,X2,X3)>
<Marked_U172(mark(X1),X2,X3) , Marked_U172(X1,X2,X3)>
<Marked_U172(X1,mark(X2),X3) , Marked_U172(X1,X2,X3)>
<Marked_U172(X1,X2,mark(X3)) , Marked_U172(X1,X2,X3)>
<Marked_U172(active(X1),X2,X3) , Marked_U172(X1,X2,X3)>
<Marked_U172(X1,active(X2),X3) , Marked_U172(X1,X2,X3)>
<Marked_U172(X1,X2,active(X3)) , Marked_U172(X1,X2,X3)>
<Marked_head(mark(X)) , Marked_head(X)>
<Marked_head(active(X)) , Marked_head(X)>
<Marked_afterNth(mark(X1),X2) , Marked_afterNth(X1,X2)>
<Marked_afterNth(X1,mark(X2)) , Marked_afterNth(X1,X2)>
<Marked_afterNth(active(X1),X2) , Marked_afterNth(X1,X2)>
<Marked_afterNth(X1,active(X2)) , Marked_afterNth(X1,X2)>
<Marked_U181(mark(X1),X2) , Marked_U181(X1,X2)>
<Marked_U181(X1,mark(X2)) , Marked_U181(X1,X2)>
<Marked_U181(active(X1),X2) , Marked_U181(X1,X2)>
<Marked_U181(X1,active(X2)) , Marked_U181(X1,X2)>
<Marked_U182(mark(X1),X2) , Marked_U182(X1,X2)>
<Marked_U182(X1,mark(X2)) , Marked_U182(X1,X2)>
<Marked_U182(active(X1),X2) , Marked_U182(X1,X2)>
<Marked_U182(X1,active(X2)) , Marked_U182(X1,X2)>
<Marked_U191(mark(X1),X2) , Marked_U191(X1,X2)>
<Marked_U191(X1,mark(X2)) , Marked_U191(X1,X2)>
<Marked_U191(active(X1),X2) , Marked_U191(X1,X2)>
<Marked_U191(X1,active(X2)) , Marked_U191(X1,X2)>
<Marked_pair(mark(X1),X2) , Marked_pair(X1,X2)>
<Marked_pair(X1,mark(X2)) , Marked_pair(X1,X2)>
<Marked_pair(active(X1),X2) , Marked_pair(X1,X2)>
<Marked_pair(X1,active(X2)) , Marked_pair(X1,X2)>
<Marked_U201(mark(X1),X2,X3,X4) , Marked_U201(X1,X2,X3,X4)>
<Marked_U201(X1,mark(X2),X3,X4) , Marked_U201(X1,X2,X3,X4)>
<Marked_U201(X1,X2,mark(X3),X4) , Marked_U201(X1,X2,X3,X4)>
<Marked_U201(X1,X2,X3,mark(X4)) , Marked_U201(X1,X2,X3,X4)>
<Marked_U201(active(X1),X2,X3,X4) , Marked_U201(X1,X2,X3,X4)>
<Marked_U201(X1,active(X2),X3,X4) , Marked_U201(X1,X2,X3,X4)>
<Marked_U201(X1,X2,active(X3),X4) , Marked_U201(X1,X2,X3,X4)>
<Marked_U201(X1,X2,X3,active(X4)) , Marked_U201(X1,X2,X3,X4)>
<Marked_U202(mark(X1),X2,X3,X4) , Marked_U202(X1,X2,X3,X4)>
<Marked_U202(X1,mark(X2),X3,X4) , Marked_U202(X1,X2,X3,X4)>
<Marked_U202(X1,X2,mark(X3),X4) , Marked_U202(X1,X2,X3,X4)>
<Marked_U202(X1,X2,X3,mark(X4)) , Marked_U202(X1,X2,X3,X4)>
<Marked_U202(active(X1),X2,X3,X4) , Marked_U202(X1,X2,X3,X4)>
<Marked_U202(X1,active(X2),X3,X4) , Marked_U202(X1,X2,X3,X4)>
<Marked_U202(X1,X2,active(X3),X4) , Marked_U202(X1,X2,X3,X4)>
<Marked_U202(X1,X2,X3,active(X4)) , Marked_U202(X1,X2,X3,X4)>
<Marked_isNatural(mark(X)) , Marked_isNatural(X)>
<Marked_isNatural(active(X)) , Marked_isNatural(X)>
<Marked_U203(mark(X1),X2,X3,X4) , Marked_U203(X1,X2,X3,X4)>
<Marked_U203(X1,mark(X2),X3,X4) , Marked_U203(X1,X2,X3,X4)>
<Marked_U203(X1,X2,mark(X3),X4) , Marked_U203(X1,X2,X3,X4)>
<Marked_U203(X1,X2,X3,mark(X4)) , Marked_U203(X1,X2,X3,X4)>
<Marked_U203(active(X1),X2,X3,X4) , Marked_U203(X1,X2,X3,X4)>
<Marked_U203(X1,active(X2),X3,X4) , Marked_U203(X1,X2,X3,X4)>
<Marked_U203(X1,X2,active(X3),X4) , Marked_U203(X1,X2,X3,X4)>
<Marked_U203(X1,X2,X3,active(X4)) , Marked_U203(X1,X2,X3,X4)>
<Marked_U204(mark(X1),X2) , Marked_U204(X1,X2)>
<Marked_U204(X1,mark(X2)) , Marked_U204(X1,X2)>
<Marked_U204(active(X1),X2) , Marked_U204(X1,X2)>
<Marked_U204(X1,active(X2)) , Marked_U204(X1,X2)>
<Marked_U21(mark(X1),X2,X3) , Marked_U21(X1,X2,X3)>
<Marked_U21(X1,mark(X2),X3) , Marked_U21(X1,X2,X3)>
<Marked_U21(X1,X2,mark(X3)) , Marked_U21(X1,X2,X3)>
<Marked_U21(active(X1),X2,X3) , Marked_U21(X1,X2,X3)>
<Marked_U21(X1,active(X2),X3) , Marked_U21(X1,X2,X3)>
<Marked_U21(X1,X2,active(X3)) , Marked_U21(X1,X2,X3)>
<Marked_U22(mark(X1),X2) , Marked_U22(X1,X2)>
<Marked_U22(X1,mark(X2)) , Marked_U22(X1,X2)>
<Marked_U22(active(X1),X2) , Marked_U22(X1,X2)>
<Marked_U22(X1,active(X2)) , Marked_U22(X1,X2)>
<Marked_U211(mark(X1),X2) , Marked_U211(X1,X2)>
<Marked_U211(X1,mark(X2)) , Marked_U211(X1,X2)>
<Marked_U211(active(X1),X2) , Marked_U211(X1,X2)>
<Marked_U211(X1,active(X2)) , Marked_U211(X1,X2)>
<Marked_U212(mark(X1),X2) , Marked_U212(X1,X2)>
<Marked_U212(X1,mark(X2)) , Marked_U212(X1,X2)>
<Marked_U212(active(X1),X2) , Marked_U212(X1,X2)>
<Marked_U212(X1,active(X2)) , Marked_U212(X1,X2)>
<Marked_U221(mark(X1),X2,X3) , Marked_U221(X1,X2,X3)>
<Marked_U221(X1,mark(X2),X3) , Marked_U221(X1,X2,X3)>
<Marked_U221(X1,X2,mark(X3)) , Marked_U221(X1,X2,X3)>
<Marked_U221(active(X1),X2,X3) , Marked_U221(X1,X2,X3)>
<Marked_U221(X1,active(X2),X3) , Marked_U221(X1,X2,X3)>
<Marked_U221(X1,X2,active(X3)) , Marked_U221(X1,X2,X3)>
<Marked_U222(mark(X1),X2,X3) , Marked_U222(X1,X2,X3)>
<Marked_U222(X1,mark(X2),X3) , Marked_U222(X1,X2,X3)>
<Marked_U222(X1,X2,mark(X3)) , Marked_U222(X1,X2,X3)>
<Marked_U222(active(X1),X2,X3) , Marked_U222(X1,X2,X3)>
<Marked_U222(X1,active(X2),X3) , Marked_U222(X1,X2,X3)>
<Marked_U222(X1,X2,active(X3)) , Marked_U222(X1,X2,X3)>
<Marked_fst(mark(X)) , Marked_fst(X)>
<Marked_fst(active(X)) , Marked_fst(X)>
<Marked_U31(mark(X1),X2,X3) , Marked_U31(X1,X2,X3)>
<Marked_U31(X1,mark(X2),X3) , Marked_U31(X1,X2,X3)>
<Marked_U31(X1,X2,mark(X3)) , Marked_U31(X1,X2,X3)>
<Marked_U31(active(X1),X2,X3) , Marked_U31(X1,X2,X3)>
<Marked_U31(X1,active(X2),X3) , Marked_U31(X1,X2,X3)>
<Marked_U31(X1,X2,active(X3)) , Marked_U31(X1,X2,X3)>
<Marked_U32(mark(X1),X2) , Marked_U32(X1,X2)>
<Marked_U32(X1,mark(X2)) , Marked_U32(X1,X2)>
<Marked_U32(active(X1),X2) , Marked_U32(X1,X2)>
<Marked_U32(X1,active(X2)) , Marked_U32(X1,X2)>
<Marked_U41(mark(X1),X2) , Marked_U41(X1,X2)>
<Marked_U41(X1,mark(X2)) , Marked_U41(X1,X2)>
<Marked_U41(active(X1),X2) , Marked_U41(X1,X2)>
<Marked_U41(X1,active(X2)) , Marked_U41(X1,X2)>
<Marked_U42(mark(X)) , Marked_U42(X)>
<Marked_U42(active(X)) , Marked_U42(X)>
<Marked_U51(mark(X1),X2) , Marked_U51(X1,X2)>
<Marked_U51(X1,mark(X2)) , Marked_U51(X1,X2)>
<Marked_U51(active(X1),X2) , Marked_U51(X1,X2)>
<Marked_U51(X1,active(X2)) , Marked_U51(X1,X2)>
<Marked_U52(mark(X)) , Marked_U52(X)>
<Marked_U52(active(X)) , Marked_U52(X)>
<Marked_U61(mark(X)) , Marked_U61(X)>
<Marked_U61(active(X)) , Marked_U61(X)>
<Marked_U71(mark(X)) , Marked_U71(X)>
<Marked_U71(active(X)) , Marked_U71(X)>
<Marked_U81(mark(X)) , Marked_U81(X)>
<Marked_U81(active(X)) , Marked_U81(X)>
<Marked_U91(mark(X)) , Marked_U91(X)>
<Marked_U91(active(X)) , Marked_U91(X)>
<Marked_isPLNat(mark(X)) , Marked_isPLNat(X)>
<Marked_isPLNat(active(X)) , Marked_isPLNat(X)>
<Marked_tail(mark(X)) , Marked_tail(X)>
<Marked_tail(active(X)) , Marked_tail(X)>
<Marked_take(mark(X1),X2) , Marked_take(X1,X2)>
<Marked_take(X1,mark(X2)) , Marked_take(X1,X2)>
<Marked_take(active(X1),X2) , Marked_take(X1,X2)>
<Marked_take(X1,active(X2)) , Marked_take(X1,X2)>
<Marked_sel(mark(X1),X2) , Marked_sel(X1,X2)>
<Marked_sel(X1,mark(X2)) , Marked_sel(X1,X2)>
<Marked_sel(active(X1),X2) , Marked_sel(X1,X2)>
<Marked_sel(X1,active(X2)) , Marked_sel(X1,X2)>
 
END GUIDED
APPLY CRITERIA (Graph splitting)
Found 54 components:

{  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
      --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(sel(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(take(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(tail(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U91(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U81(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U71(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U61(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U52(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U51(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U42(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U41(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U32(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(fst(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U212(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U211(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U22(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U204(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),X2,X3,X4))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(pair(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U191(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U182(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U181(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),mark(X2)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(head(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(head(X)) , Marked_active(head(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(s(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(s(X)) , Marked_active(s(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(natsFrom(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(cons(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U161(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U152(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U151(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U142(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U141(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U132(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U131(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U121(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),mark(X2)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(snd(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U111(X)) , Marked_mark(X)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(sel(X1,X2)) , Marked_active(sel(mark(X1),mark(X2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(take(X1,X2)) , Marked_active(take(mark(X1),mark(X2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(tail(X)) , Marked_active(tail(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isPLNat(X)) , Marked_active(isPLNat(X))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U91(X)) , Marked_active(U91(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U81(X)) , Marked_active(U81(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U71(X)) , Marked_active(U71(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U61(X)) , Marked_active(U61(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U52(X)) , Marked_active(U52(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U51(X1,X2)) , Marked_active(U51(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U42(X)) , Marked_active(U42(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U41(X1,X2)) , Marked_active(U41(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U32(X1,X2)) , Marked_active(U32(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U31(X1,X2,X3)) , Marked_active(U31(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(fst(X)) , Marked_active(fst(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U222(X1,X2,X3)) , Marked_active(U222(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U221(X1,X2,X3)) , Marked_active(U221(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U212(X1,X2)) , Marked_active(U212(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U211(X1,X2)) , Marked_active(U211(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U22(X1,X2)) , Marked_active(U22(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U21(X1,X2,X3)) , Marked_active(U21(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U204(X1,X2)) , Marked_active(U204(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U203(X1,X2,X3,X4)) , Marked_active(U203(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isNatural(X)) , Marked_active(isNatural(X))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U202(X1,X2,X3,X4)) , Marked_active(U202(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U201(X1,X2,X3,X4)) , Marked_active(U201(mark(X1),
                                                          X2,X3,X4))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(pair(X1,X2)) , Marked_active(pair(mark(X1),mark(X2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U191(X1,X2)) , Marked_active(U191(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U182(X1,X2)) , Marked_active(U182(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U181(X1,X2)) , Marked_active(U181(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(afterNth(X1,X2)) , Marked_active(afterNth(mark(X1),
                                                        mark(X2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(head(X)) , Marked_active(head(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U172(X1,X2,X3)) , Marked_active(U172(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U171(X1,X2,X3)) , Marked_active(U171(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(s(X)) , Marked_active(s(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(natsFrom(X)) , Marked_active(natsFrom(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(cons(X1,X2)) , Marked_active(cons(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U161(X1,X2)) , Marked_active(U161(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U152(X)) , Marked_active(U152(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U151(X1,X2)) , Marked_active(U151(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U142(X)) , Marked_active(U142(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U141(X1,X2)) , Marked_active(U141(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U132(X)) , Marked_active(U132(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U131(X1,X2)) , Marked_active(U131(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U121(X)) , Marked_active(U121(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X2)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(splitAt(X1,X2)) , Marked_active(splitAt(mark(X1),
                                                       mark(X2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(snd(X)) , Marked_active(snd(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U111(X)) , Marked_active(U111(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U12(X1,X2,X3)) , Marked_active(U12(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(isLNat(X)) , Marked_active(isLNat(X))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U102(X)) , Marked_active(U102(mark(X)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_mark(X1)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_mark(X1)> 
     --> <Marked_mark(U101(X1,X2)) , Marked_active(U101(mark(X1),X2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(take(N,XS)) , Marked_mark(U221(isNatural(N),N,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(tail(cons(N,XS))) , Marked_mark(U211(isNatural(N),XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(s(N),cons(X,XS))) , Marked_mark(U201(
                                                                 isNatural(
                                                                  N),
                                                                 N,X,
                                                                 XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(splitAt(0,XS)) , Marked_mark(U191(isLNat(XS),XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(snd(pair(X,Y))) , Marked_mark(U181(isLNat(X),Y))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(sel(N,XS)) , Marked_mark(U171(isNatural(N),N,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(natsFrom(N)) , Marked_mark(U161(isNatural(N),N))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(splitAt(V1,V2))) , Marked_mark(U151(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isPLNat(pair(V1,V2))) , Marked_mark(U141(isLNat(V1),V2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(sel(V1,V2))) , Marked_mark(U131(isNatural(V1),
                                                              V2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(s(V1))) , Marked_mark(U121(isNatural(V1)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isNatural(head(V1))) , Marked_mark(U111(isLNat(V1)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(take(V1,V2))) , Marked_mark(U101(isNatural(V1),
                                                            V2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(tail(V1))) , Marked_mark(U91(isLNat(V1)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(snd(V1))) , Marked_mark(U81(isPLNat(V1)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(natsFrom(V1))) , Marked_mark(U71(isNatural(V1)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(fst(V1))) , Marked_mark(U61(isPLNat(V1)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(cons(V1,V2))) , Marked_mark(U51(isNatural(V1),
                                                            V2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(isLNat(afterNth(V1,V2))) , Marked_mark(U41(isNatural(
                                                                    V1),
                                                                V2))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(head(cons(N,XS))) , Marked_mark(U31(isNatural(N),N,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(fst(pair(X,Y))) , Marked_mark(U21(isLNat(X),X,Y))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(afterNth(N,XS)) , Marked_mark(U11(isNatural(N),N,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U51(tt,V2)) , Marked_mark(U52(isLNat(V2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U41(tt,V2)) , Marked_mark(U42(isLNat(V2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U32(tt,N)) , Marked_mark(N)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U31(tt,N,XS)) , Marked_mark(U32(isLNat(XS),N))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U222(tt,N,XS)) , Marked_mark(fst(splitAt(N,XS)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U221(tt,N,XS)) , Marked_mark(U222(isLNat(XS),N,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U22(tt,X)) , Marked_mark(X)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U212(tt,XS)) , Marked_mark(XS)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U211(tt,XS)) , Marked_mark(U212(isLNat(XS),XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U21(tt,X,Y)) , Marked_mark(U22(isLNat(Y),X))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U204(pair(YS,ZS),X)) , Marked_mark(pair(cons(X,YS),ZS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U203(tt,N,X,XS)) , Marked_mark(U204(splitAt(N,XS),X))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U202(tt,N,X,XS)) , Marked_mark(U203(isLNat(XS),N,X,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U201(tt,N,X,XS)) , Marked_mark(U202(isNatural(X),
                                                        N,X,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U191(tt,XS)) , Marked_mark(pair(nil,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U182(tt,Y)) , Marked_mark(Y)>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U181(tt,Y)) , Marked_mark(U182(isLNat(Y),Y))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U172(tt,N,XS)) , Marked_mark(head(afterNth(N,XS)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U171(tt,N,XS)) , Marked_mark(U172(isLNat(XS),N,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U161(tt,N)) , Marked_mark(cons(N,natsFrom(s(N))))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U151(tt,V2)) , Marked_mark(U152(isLNat(V2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U141(tt,V2)) , Marked_mark(U142(isLNat(V2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U131(tt,V2)) , Marked_mark(U132(isLNat(V2)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U12(tt,N,XS)) , Marked_mark(snd(splitAt(N,XS)))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U11(tt,N,XS)) , Marked_mark(U12(isLNat(XS),N,XS))>
  <Marked_mark(U11(X1,X2,X3)) , Marked_active(U11(mark(X1),X2,X3))> 
     --> <Marked_active(U101(tt,V2)) , Marked_mark(U102(isLNat(V2)))>
  <Mark