proposition: Theorem mul_mals : forall a b c d : R, forall zi : FF, BND ((a - c) * b + c * (b - d)) zi -> BND (a * b - c * d) zi.
proof: Proof. intros a b c d zi Hz. replace (a * b - c * d)%R with ((a - c) * b + c * (b - d))%R. exact Hz. ring. Qed.
imports: Reals Gappa_common