Consider the following premises. ~p_12. p_2 -> s_4. p_12 <-> s_4. Can we infer p_2 from them?
 From p_12 <-> s_4, ~p_12 we can infer ~s_4. Finally, from p_2 -> s_4, ~s_4 we can infer ~p_2, which contradicts p_2. Therefore, the answer is no.