Consider the following premises. p_1 -> r. t -> p_1. r <-> t. Can we infer p_1 <-> t from them?
 From r <-> t we can infer r -> t. From p_1 -> r, r -> t we can infer p_1 -> t. Finally, from p_1 -> t, t -> p_1 we can infer p_1 <-> t. Therefore, the answer is yes.