Consider the following premises. exists y: W_4(y). forall y: W_4(y) <-> U(y). Can we infer exists y: U(y) from them?
 From forall y: W_4(y) <-> U(y) we can infer forall y: W_4(y) -> U(y). Finally, from forall y: W_4(y) -> U(y), exists y: W_4(y) we can infer exists y: U(y). Therefore, the answer is yes.