intros p0 q0 r0 H' H'0 H'1 H'2;
case (Zle_or_lt (Fexp r0) (Zmin (Fexp p0) (Fexp q0)));
auto.
intros H'3; Contradict H'2.
apply plusExact1; auto.
Qed.

Theorem plusExact2Aux :
forall p q r : float,
(0 <= p)%R ->
Fcanonic radix b p ->
Fbounded b q ->
Closest b radix (p + q) r ->
(Fexp r < Zpred (Fexp p))%Z -> r = (p + q)%R :>R.