Consider the following premises. u_2 <-> u. p -> u. u_2 -> p. Can we infer u -> p from them? If possible, name the inference rules being used at each step.
 From u_2 <-> u we can infer u -> u_2 via biconditional elimination. Finally, from u -> u_2, u_2 -> p we can infer u -> p via transitivity. Therefore, the answer is yes.