Consider the following premises. t <-> u_3. t <-> q_13. q_13 -> u_3. Can we infer u_3 <-> t from them? If possible, name the inference rules being used at each step.
 From t <-> q_13 we can infer t -> q_13 via biconditional elimination. From t -> q_13, q_13 -> u_3 we can infer t -> u_3 via transitivity. From t <-> u_3 we can infer u_3 -> t via biconditional elimination. Finally, from u_3 -> t, t -> u_3 we can infer u_3 <-> t via biconditional introduction. Therefore, the answer is yes.