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_4: ~T_1(z_4). forall z_4: U(z_4) -> T(z_4). forall z_4: T(z_4) -> U(z_4). exists z_4: U(z_4) -> T_1(z_4).
exists z_4: ~U(z_4) can be inferred via the existential modus tollens rule. exists z_4: T(z_4) -> T_1(z_4) can be inferred via the existential transitivity rule. forall z_4: U(z_4) <-> T(z_4) can be inferred via the universal biconditional introduction rule. forall z_4: T(z_4) <-> U(z_4) can be inferred via the universal biconditional introduction rule.