Consider the following premises. p_7 or ~s_2. s_2 or ~p_7. Can we infer s_2 <-> p_7 from them?
 From p_7 or ~s_2 we can infer s_2 -> p_7. From s_2 or ~p_7 we can infer p_7 -> s_2. Finally, from s_2 -> p_7, p_7 -> s_2 we can infer s_2 <-> p_7. Therefore, the answer is yes.