TIMEOUT
MAYBE
Trs:
 {  f(mark(X1), X2) -> mark(f(X1, X2)),
  f(ok(X1), ok(X2)) -> ok(f(X1, X2)),
        proper(a()) -> ok(a()),
        proper(b()) -> ok(b()),
  proper(f(X1, X2)) -> f(proper(X1), proper(X2)),
        active(b()) -> mark(a()),
  active(f(X1, X2)) -> f(active(X1), X2),
    active(f(X, X)) -> mark(f(a(), b())),
       top(mark(X)) -> top(proper(X)),
         top(ok(X)) -> top(active(X))}
 Open