TIMEOUT
MAYBE
Trs:
 {       cons(mark(X1), X2) -> cons(X1, X2),
       cons(active(X1), X2) -> cons(X1, X2),
         cons(X1, mark(X2)) -> cons(X1, X2),
       cons(X1, active(X2)) -> cons(X1, X2),
              mark(zeros()) -> active(zeros()),
                  mark(0()) -> active(0()),
         mark(cons(X1, X2)) -> active(cons(mark(X1), X2)),
              mark(tail(X)) -> active(tail(mark(X))),
            active(zeros()) -> mark(cons(0(), zeros())),
  active(tail(cons(X, XS))) -> mark(XS),
              tail(mark(X)) -> tail(X),
            tail(active(X)) -> tail(X)}
 Open