intros x y H' H'0.
rewrite <- oneZplus.
apply (oneExp_le radix); auto.
apply MSB_le_multAux; auto.
Qed.

Theorem mult_le_MSBAux :
forall x y : float,
~ is_Fzero x -> ~ is_Fzero y -> (MSB (Fmult x y) <= Zsucc (MSB x + MSB y))%Z.