Consider the following premises. U(a_21) <-> q_17. ~q_17. forall x_21: U(x_21) <-> S_21(x_21). Can we infer ~S_21(a_21) or t from them?
 From forall x_21: U(x_21) <-> S_21(x_21) we can infer U(a_21) <-> S_21(a_21). From U(a_21) <-> q_17 we can infer U(a_21) -> q_17. From U(a_21) -> q_17, ~q_17 we can infer ~U(a_21). From U(a_21) <-> S_21(a_21), ~U(a_21) we can infer ~S_21(a_21). Finally, from ~S_21(a_21) we can infer ~S_21(a_21) or t. Therefore, the answer is yes.