intros x y H' H'0 H'1 H'2 H'3.
case (Rle_or_lt y x); auto.
intros H'4; case H'4; clear H'4; intros H'4.
case FcanonicLtPos with (p := y) (q := x); auto.
intros H'5; Contradict H'3; auto with zarith.
intros H'5; elim H'5; intros H'6 H'7; clear H'5; Contradict H'3; rewrite H'6;
auto with zarith.
Contradict H'3.
rewrite FcanonicUnique with (p := x) (q := y); auto with zarith.
Qed.

Theorem FcanonicNegFexpRlt :
forall x y : float,
(x <= 0)%R ->
(y <= 0)%R -> Fcanonic x -> Fcanonic y -> (Fexp x < Fexp y)%Z -> (y < x)%R.