Consider the following premises. forall x_3: U(x_3) -> S(x_3). forall x_3: ~U(x_3). forall x_3: S(x_3) <-> U(x_3). Can we infer forall x_3: ~S(x_3) from them?
 From forall x_3: S(x_3) <-> U(x_3) we can infer forall x_3: S(x_3) -> U(x_3). From forall x_3: S(x_3) -> U(x_3), forall x_3: U(x_3) -> S(x_3) we can infer forall x_3: S(x_3) <-> U(x_3). Finally, from forall x_3: S(x_3) <-> U(x_3), forall x_3: ~U(x_3) we can infer forall x_3: ~S(x_3). Therefore, the answer is yes.