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_3: U(z_3) -> S(z_3). exists z_3: S(z_3) -> U(z_3). forall z_3: ~U(z_3).
exists z_3: ~S(z_3) can be inferred via the existential modus tollens rule. exists z_3: S(z_3) <-> U(z_3) can be inferred via the existential biconditional introduction rule. exists z_3: U(z_3) <-> S(z_3) can be inferred via the existential biconditional introduction rule.