Consider the following premises. p_3 <-> q. q <-> s_4. ~p_3. Can we infer ~s_4 from them? If possible, name the inference rules being used at each step.
 From q <-> s_4 we can infer s_4 -> q via biconditional elimination. From p_3 <-> q, ~p_3 we can infer ~q via biconditional elimination. Finally, from s_4 -> q, ~q we can infer ~s_4 via modus tollens. Therefore, the answer is yes.