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 z: U(z) -> R_3(z). forall z: ~R_3(z). exists z: R_3(z) -> U(z). forall z: P_3(z) -> U(z).
forall z: ~U(z) can be inferred via the universal modus tollens rule. forall z: P_3(z) -> R_3(z) can be inferred via the universal transitivity rule. exists z: R_3(z) <-> U(z) can be inferred via the existential biconditional introduction rule. exists z: U(z) <-> R_3(z) can be inferred via the existential biconditional introduction rule.