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