Consider the following premises. q -> t_1. t_1 <-> r_1. r_1 -> q. Can we infer r_1 <-> q from them? If possible, name the inference rules being used at each step.
 From t_1 <-> r_1 we can infer t_1 -> r_1 via biconditional elimination. From q -> t_1, t_1 -> r_1 we can infer q -> r_1 via transitivity. Finally, from r_1 -> q, q -> r_1 we can infer r_1 <-> q via biconditional introduction. Therefore, the answer is yes.