TRS:
 {    +(0(), y) -> y,
     +(s(x), y) -> s(+(x, y)),
      -(0(), y) -> 0(),
      -(x, 0()) -> x,
  -(s(x), s(y)) -> -(x, y)}
 MPO:
  Prec:
   + > s
   empty
  Strict:
   {}
   Weak:
    {}
  Qed