Consider the following premises. p_6 <-> u_3. ~r_2. u_3 -> q_11. p_6 -> r_2. q_11 -> u_3. Can we infer ~q_11 from them?
 From u_3 -> q_11, q_11 -> u_3 we can infer u_3 <-> q_11. From p_6 -> r_2, ~r_2 we can infer ~p_6. From p_6 <-> u_3, ~p_6 we can infer ~u_3. Finally, from u_3 <-> q_11, ~u_3 we can infer ~q_11. Therefore, the answer is yes.