Consider the following premises. p_4 <-> s. p_4 <-> w_3. ~w_3. Can we infer s from them? If possible, name the inference rules being used at each step.
 From p_4 <-> w_3, ~w_3 we can infer ~p_4 via biconditional elimination. Finally, from p_4 <-> s, ~p_4 we can infer ~s via biconditional elimination, which contradicts s. Therefore, the answer is no.