Consider the following premises. u_2 or s_1. ~u_2 or u. u -> p. s_1 -> p. Can we infer ~p from them?
 From u_2 or s_1, ~u_2 or u we can infer s_1 or u. Finally, from s_1 -> p, u -> p, s_1 or u we can infer p, which contradicts ~p. Therefore, the answer is no.