Consider the following premises. forall x: W_1(x) <-> S(x). u -> W_1(a_5). forall x: ~S(x). Can we infer ~u from them? If possible, name the inference rules being used at each step.
 From forall x: W_1(x) <-> S(x), forall x: ~S(x) we can infer forall x: ~W_1(x) via universal biconditional elimination. From forall x: ~W_1(x) we can infer ~W_1(a_5) via universal instantiation. Finally, from u -> W_1(a_5), ~W_1(a_5) we can infer ~u via modus tollens. Therefore, the answer is yes.