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