Consider the following premises. p_13 <-> s_3. s -> r. s_3 -> s. r <-> p_13. Can we infer s_3 <-> p_13 from them?
 From s_3 -> s, s -> r we can infer s_3 -> r. From p_13 <-> s_3 we can infer p_13 -> s_3. From r <-> p_13 we can infer r -> p_13. From s_3 -> r, r -> p_13 we can infer s_3 -> p_13. Finally, from s_3 -> p_13, p_13 -> s_3 we can infer s_3 <-> p_13. Therefore, the answer is yes.