ifftrueMarked_fperfectpminusMarked_perfectp0slefalsezyxuperfectp(0)falseperfectp(s(x))f(x,s(0),s(x),s(x))f(0,y,0,u)truef(0,y,s(z),u)falsef(s(x),0,z,u)f(x,u,minus(z,s(x)),u)f(s(x),s(y),z,u)if(le(x,y),f(s(x),minus(y,x),z,u),f(x,u,z,u))perfectp(0)falseperfectp(s(x))f(x,s(0),s(x),s(x))f(0,y,0,u)truef(0,y,s(z),u)falsef(s(x),0,z,u)f(x,u,minus(z,s(x)),u)f(s(x),s(y),z,u)if(le(x,y),f(s(x),minus(y,x),z,u),f(x,u,z,u))Marked_perfectp(s(x))Marked_f(x,s(0),s(x),s(x))Marked_f(s(x),0,z,u)Marked_f(x,u,minus(z,s(x)),u)Marked_f(s(x),s(y),z,u)Marked_f(s(x),minus(y,x),z,u)Marked_f(s(x),s(y),z,u)Marked_f(x,u,z,u)perfectp(0)falseperfectp(s(x))f(x,s(0),s(x),s(x))f(0,y,0,u)truef(0,y,s(z),u)falsef(s(x),0,z,u)f(x,u,minus(z,s(x)),u)f(s(x),s(y),z,u)if(le(x,y),f(s(x),minus(y,x),z,u),f(x,u,z,u))Marked_f(s(x),0,z,u)Marked_f(x,u,minus(z,s(x)),u)Marked_f(s(x),s(y),z,u)Marked_f(x,u,z,u)Marked_f1Marked_f(s(x),s(y),z,u)Marked_f(x,u,z,u)Marked_f(s(x),0,z,u)Marked_f(x,u,minus(z,s(x)),u)perfectp(0)falseperfectp(s(x))f(x,s(0),s(x),s(x))f(0,y,0,u)truef(0,y,s(z),u)falsef(s(x),0,z,u)f(x,u,minus(z,s(x)),u)f(s(x),s(y),z,u)if(le(x,y),f(s(x),minus(y,x),z,u),f(x,u,z,u))