Consider the following premises. u -> s_3. s_3 -> u. p -> s_3. ~u. Can we infer p from them?
 From s_3 -> u, u -> s_3 we can infer s_3 <-> u. From s_3 <-> u, ~u we can infer ~s_3. Finally, from p -> s_3, ~s_3 we can infer ~p, which contradicts p. Therefore, the answer is no.