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