Consider the following premises. ~u. p_1 <-> p. u or ~p_1. Can we infer ~p from them? If possible, name the inference rules being used at each step.
 From u or ~p_1 we can infer p_1 -> u via rewriting. From p_1 -> u, ~u we can infer ~p_1 via modus tollens. Finally, from p_1 <-> p, ~p_1 we can infer ~p via biconditional elimination. Therefore, the answer is yes.