Consider the following premises. forall y: U_3(y) <-> R(y). forall y: R(y) -> U_3(y). Can we infer exists y: ~(R(y) <-> U_3(y)) from them?
 From forall y: U_3(y) <-> R(y) we can infer forall y: U_3(y) -> R(y). Finally, from forall y: R(y) -> U_3(y), forall y: U_3(y) -> R(y) we can infer forall y: R(y) <-> U_3(y), which contradicts exists y: ~(R(y) <-> U_3(y)). Therefore, the answer is no.