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