Consider the following premises. U(a_4) -> r. forall z: W(z) -> U(z). r -> W(a_4). Can we infer r -> U(a_4) from them?
 From forall z: W(z) -> U(z) we can infer W(a_4) -> U(a_4). Finally, from r -> W(a_4), W(a_4) -> U(a_4) we can infer r -> U(a_4). Therefore, the answer is yes.