Consider the following premises. q_3 -> r_6. p_6 -> q_3. q -> p_6. r_6 -> q. Can we infer r_6 <-> p_6 from them? If possible, name the inference rules being used at each step.
 From p_6 -> q_3, q_3 -> r_6 we can infer p_6 -> r_6 via transitivity. From r_6 -> q, q -> p_6 we can infer r_6 -> p_6 via transitivity. Finally, from r_6 -> p_6, p_6 -> r_6 we can infer r_6 <-> p_6 via biconditional introduction. Therefore, the answer is yes.