What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: forall x_4: ~R_1(x_4). exists x_4: R_1(x_4) <-> U_2(x_4).
exists x_4: R_1(x_4) -> U_2(x_4) can be inferred via the existential biconditional elimination rule. exists x_4: U_2(x_4) -> R_1(x_4) can be inferred via the existential biconditional elimination rule. exists x_4: ~U_2(x_4) can be inferred via the existential biconditional elimination rule.