intros p z H' H'0;
apply
Rlt_le_trans with (FtoR radix (Float (Zpos (vNum b)) (Zpred z))).
unfold FtoRradix in |- *; apply maxMax; auto with zarith;
unfold Zpred in |- *; auto with zarith.
unfold FtoRradix, FtoR, nNormMin in |- *; simpl in |- *.
pattern z at 2 in |- *; replace z with (Zsucc (Zpred z));
[ rewrite powerRZ_Zs; auto with real zarith
| unfold Zsucc, Zpred in |- *; ring ].
rewrite <- Rmult_assoc.
apply Rmult_le_compat_r; auto with real arith.
pattern radix at 2 in |- *; rewrite <- (Zpower_nat_1 radix).
rewrite <- Rmult_IZR.
rewrite <- Zpower_nat_is_exp.
replace (pred precision + 1) with precision.
replace (INR (nat_of_P (vNum b))) with (IZR (Zpos (vNum b))).
rewrite pGivesBound; auto with real.
simpl; unfold IZR; rewrite <- INR_IPR; auto.
generalize precisionNotZero; case precision; simpl in |- *; auto with arith.
intros H'1; Contradict H'1; auto.
intros; rewrite plus_comm; simpl in |- *; auto.
Qed.

Theorem FnormalLtFirstNormalPos :
forall p : float, Fnormal p -> (0 <= p)%R -> (firstNormalPos <= p)%R.