Consider the following premises. r_1 -> p_15. q_15 -> r_1. q_15 -> r_1. p_15 <-> q_15. Can we infer r_1 <-> q_15 from them?
 From p_15 <-> q_15 we can infer p_15 -> q_15. From r_1 -> p_15, p_15 -> q_15 we can infer r_1 -> q_15. Finally, from r_1 -> q_15, q_15 -> r_1 we can infer r_1 <-> q_15. Therefore, the answer is yes.