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