Consider the following premises. w <-> u. ~p_9. p_9 <-> u. Can we infer w from them?
 From p_9 <-> u we can infer u -> p_9. From u -> p_9, ~p_9 we can infer ~u. Finally, from w <-> u, ~u we can infer ~w, which contradicts w. Therefore, the answer is no.