Consider the following premises. q_6 -> p_11. p_11 -> q_6. ~t. p_11 <-> t. Can we infer ~q_6 from them?
 From p_11 <-> t, ~t we can infer ~p_11. From p_11 -> q_6, q_6 -> p_11 we can infer p_11 <-> q_6. From p_11 <-> q_6 we can infer q_6 -> p_11. Finally, from q_6 -> p_11, ~p_11 we can infer ~q_6. Therefore, the answer is yes.