Consider the following premises. t_4 or p_4. p_9 <-> t_4. ~u. p_9 <-> u. Can we infer p_4 from them?
 From p_9 <-> u, ~u we can infer ~p_9. From p_9 <-> t_4, ~p_9 we can infer ~t_4. Finally, from t_4 or p_4, ~t_4 we can infer p_4. Therefore, the answer is yes.