Consider the following premises. r_2 <-> s_2. r_2 <-> s_2. Can we infer s_2 <-> r_2 from them?
 From r_2 <-> s_2 we can infer r_2 -> s_2. From r_2 <-> s_2 we can infer s_2 -> r_2. Finally, from s_2 -> r_2, r_2 -> s_2 we can infer s_2 <-> r_2. Therefore, the answer is yes.