Consider the following premises. ~q_4. p_11 -> q_4. p_11 or ~q_7. u <-> q_7. Can we infer ~u from them? If possible, name the inference rules being used at each step.
 From p_11 -> q_4, ~q_4 we can infer ~p_11 via modus tollens. From p_11 or ~q_7 we can infer q_7 -> p_11 via rewriting. From q_7 -> p_11, ~p_11 we can infer ~q_7 via modus tollens. Finally, from u <-> q_7, ~q_7 we can infer ~u via biconditional elimination. Therefore, the answer is yes.