Consider the following premises. ~s. t -> s. t_1 -> p_11. t_1 <-> t. p_11 -> t_1. Can we infer ~p_11 from them?
 From p_11 -> t_1, t_1 -> p_11 we can infer p_11 <-> t_1. From t -> s, ~s we can infer ~t. From t_1 <-> t, ~t we can infer ~t_1. Finally, from p_11 <-> t_1, ~t_1 we can infer ~p_11. Therefore, the answer is yes.