Consider the following premises. ~q_7. p_7 -> q_7. ~p_7 <-> s_4. Can we infer s_4 from them? If possible, name the inference rules being used at each step.
 From p_7 -> q_7, ~q_7 we can infer ~p_7 via modus tollens. From ~p_7 <-> s_4 we can infer ~p_7 -> s_4 via biconditional elimination. Finally, from ~p_7 -> s_4, ~p_7 we can infer s_4 via modus ponens. Therefore, the answer is yes.