Marked_plusplussandMarked_activatett0Marked_andactivateMNXand(tt,X)activate(X)plus(N,0)Nplus(N,s(M))s(plus(N,M))activate(X)Xand(tt,X)activate(X)plus(N,0)Nplus(N,s(M))s(plus(N,M))activate(X)XMarked_and(tt,X)Marked_activate(X)Marked_plus(N,s(M))Marked_plus(N,M)and(tt,X)activate(X)plus(N,0)Nplus(N,s(M))s(plus(N,M))activate(X)XMarked_plus(N,s(M))Marked_plus(N,M)activate120020tt30and3330s210plus320Marked_plus30