Consider the following premises. u_4 <-> q_4. p_9 <-> u_4. Can we infer q_4 -> p_9 from them? If possible, name the inference rules being used at each step.
 From p_9 <-> u_4 we can infer u_4 -> p_9 via biconditional elimination. From u_4 <-> q_4 we can infer q_4 -> u_4 via biconditional elimination. Finally, from q_4 -> u_4, u_4 -> p_9 we can infer q_4 -> p_9 via transitivity. Therefore, the answer is yes.