Consider the following premises. w -> q. p_4 -> w. q -> t. t -> p_4. Can we infer p_4 <-> q from them? If possible, name the inference rules being used at each step.
 From p_4 -> w, w -> q we can infer p_4 -> q via transitivity. From q -> t, t -> p_4 we can infer q -> p_4 via transitivity. Finally, from p_4 -> q, q -> p_4 we can infer p_4 <-> q via biconditional introduction. Therefore, the answer is yes.