proposition: Theorem add_firq : forall a b c : R, forall zi : FF, NZR (c + b) -> BND ((a - c) / (c + b)) zi -> BND (((a + b) - (c + b)) / (c + b)) zi.
proof: Proof. intros a b c zi Hac Hz. replace (((a + b) - (c + b)) / (c + b))%R with ((a - c) / (c + b))%R. exact Hz. field. exact Hac. Qed.
imports: Reals Gappa_common