intros x y H' H'0 H'1 H'2 H'3.
case (Rle_or_lt x y); intros Le2; auto.
apply oppBoundedInv; auto.
rewrite Fopp_Fminus.
apply BminusSameExpAux; auto.
apply BminusSameExpAux; auto with real.
Qed.

Theorem BminusSameExpNeg :
forall x y : float,
Fbounded b x ->
Fbounded b y ->
(x <= 0)%R -> (y <= 0)%R -> Fexp x = Fexp y -> Fbounded b (Fminus radix x y).