What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? forall z: U(z) -> S(z). forall z: S(z) -> U(z). exists z: U(z) -> S(z).
forall z: U(z) <-> S(z). forall z: S(z) <-> U(z). exists z: U(z) <-> S(z). exists z: S(z) <-> U(z).