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) -> U_1(z). exists z: ~U_1(z). forall z: U_1(z) -> U(z).
exists z: ~U(z). forall z: U(z) <-> U_1(z). forall z: U_1(z) <-> U(z).