Consider the following premises. ~u. p_1 <-> p. u or ~p_1. Can we infer ~p from them?
 From u or ~p_1 we can infer p_1 -> u. From p_1 -> u, ~u we can infer ~p_1. Finally, from p_1 <-> p, ~p_1 we can infer ~p. Therefore, the answer is yes.