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