Consider the following premises. forall z_1: S(z_1) or ~T(z_1). forall z_1: S(z_1) <-> T(z_1). Can we infer forall z_1: S(z_1) <-> T(z_1) from them? If possible, name the inference rules being used at each step.
That is one of the premises. Therefore, the answer is yes.