TIMEOUT
MAYBE
Trs:
 {     top(sent(x)) -> top(check(rest(x))),
        rest(nil()) -> sent(nil()),
   rest(cons(x, y)) -> sent(y),
     check(sent(x)) -> sent(check(x)),
     check(rest(x)) -> rest(check(x)),
  check(cons(x, y)) -> cons(check(x), y),
  check(cons(x, y)) -> cons(x, check(y)),
  check(cons(x, y)) -> cons(x, y)}
 Open