Consider the following premises. s_1 <-> u_3. ~u_3. p_15 or q. q -> p. p_15 -> p. Can we infer s_1 from them?
 From p_15 -> p, q -> p, p_15 or q we can infer p. Finally, from s_1 <-> u_3, ~u_3 we can infer ~s_1, which contradicts s_1. Therefore, the answer is no.