Consider the following premises. Q_9(a_8) -> u. u <-> P_9(a_8). forall x_9: P_9(x_9). Can we infer u from them? If possible, name the inference rules being used at each step.
 From forall x_9: P_9(x_9) we can infer forall x_9: P_9(x_9) or Q_9(x_9) via universal addition. From forall x_9: P_9(x_9) or Q_9(x_9) we can infer P_9(a_8) or Q_9(a_8) via universal instantiation. From u <-> P_9(a_8) we can infer P_9(a_8) -> u via biconditional elimination. Finally, from P_9(a_8) -> u, Q_9(a_8) -> u, P_9(a_8) or Q_9(a_8) we can infer u via disjunction elimination. Therefore, the answer is yes.