nope, let

now, consider some integer , and take . then we have , but

you may also consider the contrapostive. it would probably be more straight forward to you. just make sure you know what the negation of an implication is

this is true, and provable. give a direct proof of the (<=) direction and a proof by contrapositive of the (=>) directionb) (SxT)xU = Sx(TxU) <=====>