Consider the following premises. w_3 -> q_8. q_8 -> u. u -> w_3. u -> w_3. Can we infer u <-> w_3 from them? If possible, name the inference rules being used at each step.
 From w_3 -> q_8, q_8 -> u we can infer w_3 -> u via transitivity. Finally, from u -> w_3, w_3 -> u we can infer u <-> w_3 via biconditional introduction. Therefore, the answer is yes.