TRS:
 {              merge(x, nil()) -> x,
                merge(nil(), y) -> y,
  merge(++(x, y), ++(u(), v())) -> ++(x, merge(y, ++(u(), v()))),
  merge(++(x, y), ++(u(), v())) -> ++(u(), merge(++(x, y), v()))}
 MPO:
  Prec:
   merge > ++
   empty
  Strict:
   {}
   Weak:
    {}
  Qed