Definition Zrnd_opp x := Zopp (rnd (-x)).Global Instance valid_rnd_opp : Valid_rnd Zrnd_opp.

(* Specifications: *)
Theorem round_opp : forall x, round rnd (- x) = Ropp (round Zrnd_opp x).
Theorem round_opp : forall x, round rnd (- x) = Ropp (round Zrnd_opp x).