Consider the following premises. q -> p_7. p_3 <-> q. s. p_7 -> ~s. Can we infer p_3 from them?
 From p_7 -> ~s, s we can infer ~p_7. From q -> p_7, ~p_7 we can infer ~q. Finally, from p_3 <-> q, ~q we can infer ~p_3, which contradicts p_3. Therefore, the answer is no.