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_2: ~Q_2(x_2). forall x_2: U(x_2) -> R(x_2). forall x_2: R(x_2) -> U(x_2). exists x_2: U(x_2) -> Q_2(x_2).
exists x_2: ~U(x_2) can be inferred via the existential modus tollens rule. exists x_2: R(x_2) -> Q_2(x_2) can be inferred via the existential transitivity rule. forall x_2: U(x_2) <-> R(x_2) can be inferred via the universal biconditional introduction rule. forall x_2: R(x_2) <-> U(x_2) can be inferred via the universal biconditional introduction rule.