Consider the following premises. Q_8(a_7) -> P_8(a_7). forall x_8: Q_8(x_8) -> P_8(x_8). forall x_8: P_8(x_8) -> Q_8(x_8). Can we infer ~(P_8(a_7) <-> Q_8(a_7)) from them?
That contradicts the premises. Therefore the answer is no.