Consider the following premises. r_1 -> q_13. u_4 <-> r_1. u_4. q_13 -> u_4. Can we infer r_1 from them?
 From r_1 -> q_13, q_13 -> u_4 we can infer r_1 -> u_4. From u_4 <-> r_1 we can infer u_4 -> r_1. From r_1 -> u_4, u_4 -> r_1 we can infer r_1 <-> u_4. From r_1 <-> u_4 we can infer u_4 -> r_1. Finally, from u_4 -> r_1, u_4 we can infer r_1. Therefore, the answer is yes.