TIMEOUT
MAYBE
Trs:
 {            s(s(x)) -> x,
           s(f(x, y)) -> f(s(y), s(x)),
           s(g(x, y)) -> g(s(x), s(y)),
               s(a()) -> a(),
  f(g(x, y), g(u, v)) -> g(f(x, u), f(y, v)),
            f(a(), y) -> y,
            f(x, a()) -> x,
          g(a(), a()) -> a()}
 Open