Consider the following premises. ~q_12. p_12 <-> q_12. Can we infer ~p_12 or u from them?
 From p_12 <-> q_12 we can infer p_12 -> q_12. From p_12 -> q_12, ~q_12 we can infer ~p_12. Finally, from ~p_12 we can infer ~p_12 or u. Therefore, the answer is yes.