Consider the following premises. ~p_8. q_8 <-> r_4. p_8 <-> q_8. Can we infer ~r_4 from them? If possible, name the inference rules being used at each step.
 From p_8 <-> q_8, ~p_8 we can infer ~q_8 via biconditional elimination. From q_8 <-> r_4 we can infer r_4 -> q_8 via biconditional elimination. Finally, from r_4 -> q_8, ~q_8 we can infer ~r_4 via modus tollens. Therefore, the answer is yes.