MAYBE

Problem:
 active(zeros()) -> mark(cons(0(),zeros()))
 active(and(tt(),X)) -> mark(X)
 active(length(nil())) -> mark(0())
 active(length(cons(N,L))) -> mark(s(length(L)))
 mark(zeros()) -> active(zeros())
 mark(cons(X1,X2)) -> active(cons(mark(X1),X2))
 mark(0()) -> active(0())
 mark(and(X1,X2)) -> active(and(mark(X1),X2))
 mark(tt()) -> active(tt())
 mark(length(X)) -> active(length(mark(X)))
 mark(nil()) -> active(nil())
 mark(s(X)) -> active(s(mark(X)))
 cons(mark(X1),X2) -> cons(X1,X2)
 cons(X1,mark(X2)) -> cons(X1,X2)
 cons(active(X1),X2) -> cons(X1,X2)
 cons(X1,active(X2)) -> cons(X1,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)
 length(mark(X)) -> length(X)
 length(active(X)) -> length(X)
 s(mark(X)) -> s(X)
 s(active(X)) -> s(X)

Proof:
 Open