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