Consider the following premises. q_8 <-> s. p_8 <-> q_8. ~p_8. u <-> s. Can we infer ~u from them?
 From p_8 <-> q_8, ~p_8 we can infer ~q_8. From q_8 <-> s, ~q_8 we can infer ~s. Finally, from u <-> s, ~s we can infer ~u. Therefore, the answer is yes.