MAYBE

Problem:
 active(and(tt(),X)) -> mark(X)
 active(plus(N,0())) -> mark(N)
 active(plus(N,s(M))) -> mark(s(plus(N,M)))
 active(x(N,0())) -> mark(0())
 active(x(N,s(M))) -> mark(plus(x(N,M),N))
 mark(and(X1,X2)) -> active(and(mark(X1),X2))
 mark(tt()) -> active(tt())
 mark(plus(X1,X2)) -> active(plus(mark(X1),mark(X2)))
 mark(0()) -> active(0())
 mark(s(X)) -> active(s(mark(X)))
 mark(x(X1,X2)) -> active(x(mark(X1),mark(X2)))
 and(mark(X1),X2) -> and(X1,X2)
 and(X1,mark(X2)) -> and(X1,X2)
 and(active(X1),X2) -> and(X1,X2)
 and(X1,active(X2)) -> and(X1,X2)
 plus(mark(X1),X2) -> plus(X1,X2)
 plus(X1,mark(X2)) -> plus(X1,X2)
 plus(active(X1),X2) -> plus(X1,X2)
 plus(X1,active(X2)) -> plus(X1,X2)
 s(mark(X)) -> s(X)
 s(active(X)) -> s(X)
 x(mark(X1),X2) -> x(X1,X2)
 x(X1,mark(X2)) -> x(X1,X2)
 x(active(X1),X2) -> x(X1,X2)
 x(X1,active(X2)) -> x(X1,X2)

Proof:
 Open