Consider the following premises. s_4 <-> q_8. ~p_4. p_4 <-> q_8. Can we infer ~s_4 from them? If possible, name the inference rules being used at each step.
 From p_4 <-> q_8, ~p_4 we can infer ~q_8 via biconditional elimination. From s_4 <-> q_8 we can infer s_4 -> q_8 via biconditional elimination. Finally, from s_4 -> q_8, ~q_8 we can infer ~s_4 via modus tollens. Therefore, the answer is yes.