Consider the following premises. u -> p_1. u <-> q_9. p_1 -> q_9. Can we infer u <-> p_1 from them? If possible, name the inference rules being used at each step.
 From u <-> q_9 we can infer q_9 -> u via biconditional elimination. From p_1 -> q_9, q_9 -> u we can infer p_1 -> u via transitivity. Finally, from u -> p_1, p_1 -> u we can infer u <-> p_1 via biconditional introduction. Therefore, the answer is yes.