Consider the following premises. p_9 -> r. p_9 <-> q_13. r <-> q_13. Can we infer q_13 <-> r from them? If possible, name the inference rules being used at each step.
 From r <-> q_13 we can infer r -> q_13 via biconditional elimination. From p_9 <-> q_13 we can infer q_13 -> p_9 via biconditional elimination. From q_13 -> p_9, p_9 -> r we can infer q_13 -> r via transitivity. Finally, from q_13 -> r, r -> q_13 we can infer q_13 <-> r via biconditional introduction. Therefore, the answer is yes.