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.