Consider the following premises. forall x_6: P_1(x_6) -> Q_6(x_6). R_6(a_5) -> u. forall x_6: Q_6(x_6) -> R_6(x_6). Can we infer ~(P_1(a_5) -> u) from them? If possible, name the inference rules being used at each step.
That contradicts the premises. Therefore the answer is no.