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