rewrite Fplus_correct.
rewrite Fopp_correct; auto.
Qed.

Theorem Fopp_Fminus : forall p q : float, Fopp (Fminus p q) = Fminus q p.
intros p q; case p; case q; unfold Fopp, Fminus, Fplus in |- *; simpl in |- *;
auto.