intros b p n H'; repeat split; simpl in |- *; auto with float.
apply Zle_trans with (Fexp p); auto with float.
pattern (Fexp p) at 1 in |- *;
(replace (Fexp p) with (Fexp p + 0%nat)%Z; [ idtac | simpl in |- *; ring ]).
apply Zplus_le_compat_l.
apply inj_le; auto with arith.
Qed.

Theorem FvalScale :
forall (b : Fbound) (p : float) (n : nat),
Float (Fnum p) (Fexp p + n) = (powerRZ radix n * p)%R :>R.