Theorem errorBoundedPlusLe : forall p q pq : float, Fbounded b p -> Fbounded b q -> (Fexp p <= Fexp q)%Z -> Closest b radix (p + q) pq -> exists error : float, error = Rabs (p + q - pq) :>R /\ Fbounded b error /\ Fexp error = Zmin (Fexp p) (Fexp q).