Consider the following premises. r <-> t. t -> p_1. p_1 -> r. Can we infer p_1 <-> t from them? If possible, name the inference rules being used at each step.
 From r <-> t we can infer r -> t via biconditional elimination. From p_1 -> r, r -> t we can infer p_1 -> t via transitivity. Finally, from p_1 -> t, t -> p_1 we can infer p_1 <-> t via biconditional introduction. Therefore, the answer is yes.