What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? forall x: U(x) -> R_4(x). forall x: U(x) or R(x). exists x: R_4(x) <-> R(x).
exists x: R_4(x) -> R(x). exists x: R(x) -> R_4(x).