Consider the following premises. forall z: W(z) or ~S(z). forall z: W(z) -> S(z). Can we infer forall z: S(z) <-> W(z) from them? If possible, name the inference rules being used at each step.
 From forall z: W(z) or ~S(z) we can infer forall z: S(z) -> W(z) via universal rewriting. Finally, from forall z: S(z) -> W(z), forall z: W(z) -> S(z) we can infer forall z: S(z) <-> W(z) via universal biconditional introduction. Therefore, the answer is yes.