proposition: Theorem mul_on : forall x y : R, forall xi yi zi : FF, BND x xi -> BND y yi -> mul_no_helper yi xi zi = true -> BND (x * y) zi.
proof: Proof. intros x y xi yi zi Hx Hy Hb. rewrite Rmult_comm. exact (mul_no _ _ _ _ _ Hy Hx Hb). Qed.
imports: Gappa_common Gappa_decimal