Consider the following premises. r -> w_1. r_1 -> r. w_1 -> r_1. Can we infer r <-> r_1 from them? If possible, name the inference rules being used at each step.
 From r -> w_1, w_1 -> r_1 we can infer r -> r_1 via transitivity. Finally, from r -> r_1, r_1 -> r we can infer r <-> r_1 via biconditional introduction. Therefore, the answer is yes.