Consider the following premises. p_15 or t_1. p_15 <-> u_2. ~u_2. Can we infer s_2 or t_1 from them?
 From p_15 <-> u_2 we can infer p_15 -> u_2. From p_15 -> u_2, ~u_2 we can infer ~p_15. From ~p_15 we can infer ~p_15 or s_2. Finally, from ~p_15 or s_2, p_15 or t_1 we can infer s_2 or t_1. Therefore, the answer is yes.