Consider the following premises. t -> s. w_4 <-> s. ~w_4. Can we infer t from them? If possible, name the inference rules being used at each step.
 From w_4 <-> s we can infer s -> w_4 via biconditional elimination. From t -> s, s -> w_4 we can infer t -> w_4 via transitivity. Finally, from t -> w_4, ~w_4 we can infer ~t via modus tollens, which contradicts t. Therefore, the answer is no.