pattern radix at 1 in |- *; rewrite <- (Zpower_nat_1 radix);
unfold nNormMin in |- *; auto with zarith.
apply nNormMimLtvNum; auto with zarith.
Qed.

Theorem RoundBound :
forall x y p : float,
Fbounded b x ->
Fbounded b y ->
Fbounded b p ->
Closest b radix (x + y) p ->
(radix < 2%nat * pPred (vNum b))%Z ->
(Rabs p <=
Rabs (x + y) *
(2%nat * pPred (vNum b) * / (2%nat * pPred (vNum b) - radix)))%R.