intros b x H'; repeat split; simpl in |- *; auto with float zarith.
replace (Zabs (- Fnum x)) with (Zabs (Fnum x)); auto with float.
case (Fnum x); simpl in |- *; auto.
Qed.

(* Specifications: *)
Theorem oppBoundedInv :
forall (b : Fbound) (x : float), Fbounded b (Fopp x) -> Fbounded b x.