Consider the following premises. p_7 or ~u. u or ~p_7. Can we infer ~(u <-> p_7) from them?
 From p_7 or ~u we can infer u -> p_7. From u or ~p_7 we can infer p_7 -> u. Finally, from u -> p_7, p_7 -> u we can infer u <-> p_7, which contradicts ~(u <-> p_7). Therefore, the answer is no.