Consider the following premises. w_2. s_4 -> ~w_2. t <-> s_4. Can we infer t from them? If possible, name the inference rules being used at each step.
 From s_4 -> ~w_2, w_2 we can infer ~s_4 via modus tollens. Finally, from t <-> s_4, ~s_4 we can infer ~t via biconditional elimination, which contradicts t. Therefore, the answer is no.