Consider the following premises. P_8(a_5). forall x_8: P_8(x_8) <-> Q_8(x_8). Can we infer Q_8(a_5) from them?
 From forall x_8: P_8(x_8) <-> Q_8(x_8) we can infer forall x_8: P_8(x_8) -> Q_8(x_8). From forall x_8: P_8(x_8) -> Q_8(x_8) we can infer P_8(a_5) -> Q_8(a_5). Finally, from P_8(a_5) -> Q_8(a_5), P_8(a_5) we can infer Q_8(a_5). Therefore, the answer is yes.