intros x; unfold is_Fzero, Fulp, Fnormalize in |- *; case (Z_zerop (Fnum x));
simpl in |- *; auto.
intros H' H'0; Contradict H'; auto.
Qed.

Theorem FulpLe2 :
forall p : float,
Fbounded b p ->
Fnormal radix b (Fnormalize radix b precision p) ->
(Fulp p <= Rabs p * powerRZ radix (Zsucc (- precision)))%R.