Consider the following premises. r_3 -> p_1. q_6 -> r_3. p_6 -> q_6. p_1 -> p_6. Can we infer r_3 <-> p_1 from them?
 From p_6 -> q_6, q_6 -> r_3 we can infer p_6 -> r_3. From p_1 -> p_6, p_6 -> r_3 we can infer p_1 -> r_3. Finally, from r_3 -> p_1, p_1 -> r_3 we can infer r_3 <-> p_1. Therefore, the answer is yes.