proposition: Theorem ulp_opp : forall x, ulp (- x) = ulp x.
proof: Proof. intros x. unfold ulp. case Req_bool_spec; intros H1. rewrite Req_bool_true; trivial. rewrite <- (Ropp_involutive x), H1; ring. rewrite Req_bool_false. now rewrite cexp_opp. intros H2; apply H1; rewrite H2; ring. Qed.
imports: Coq(ZArith Reals Psatz) Zaux Raux Defs Round_pred Generic_fmt Float_prop