What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? exists x: ~U(x). forall x: R_3(x) or U_2(x). forall x: R_3(x) <-> U(x).
forall x: R_3(x) -> U(x). forall x: U(x) -> R_3(x). exists x: ~R_3(x).