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: exists x_2: Q_2(x_2) -> R(x_2). forall x_2: ~R(x_2). forall x_2: R(x_2) -> Q_2(x_2).
exists x_2: ~Q_2(x_2) can be inferred via the existential modus tollens rule. exists x_2: Q_2(x_2) <-> R(x_2) can be inferred via the existential biconditional introduction rule. exists x_2: R(x_2) <-> Q_2(x_2) can be inferred via the existential biconditional introduction rule.