intros; rewrite Zopp_involutive; auto.
Qed.

Theorem Fzero_opp : forall f : float, ~ is_Fzero f -> ~ is_Fzero (Fopp f).
intros f; case f; intros n e; case n; unfold is_Fzero in |- *; simpl in |- *;
auto with zarith; intros; red in |- *; intros; discriminate.