Consider the following premises. forall z_3: P_4(z_3) <-> Q(z_3). forall z_3: P_4(z_3) -> Q(z_3). forall z_3: Q(z_3) -> P_4(z_3). Can we infer forall z_3: P_4(z_3) <-> Q(z_3) from them? If possible, name the inference rules being used at each step.
That is one of the premises. Therefore, the answer is yes.