Consider the following premises. ~q. p_7. p_7 <-> q. Can we infer s from them?
 From p_7 <-> q, ~q we can infer ~p_7. From p_7 we can infer p_7 or s. Finally, from p_7 or s, ~p_7 we can infer s. Therefore, the answer is yes. Notice, however, that the premises were contradictory, so we can infer anything from them.