TRS:
 {    minus(x, 0()) -> x,
  minus(s(x), s(y)) -> minus(x, y),
             f(0()) -> s(0()),
            f(s(x)) -> minus(s(x), g(f(x))),
             g(0()) -> 0(),
            g(s(x)) -> minus(s(x), f(g(x)))}
 Fail