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_6: T_3(x_6) -> S(x_6). forall x_6: S(x_6) -> T_3(x_6). forall x_6: ~Q_1(x_6). forall x_6: S(x_6) -> Q_1(x_6).
forall x_6: ~S(x_6) can be inferred via the universal modus tollens rule. exists x_6: T_3(x_6) -> Q_1(x_6) can be inferred via the existential transitivity rule. exists x_6: T_3(x_6) <-> S(x_6) can be inferred via the existential biconditional introduction rule. exists x_6: S(x_6) <-> T_3(x_6) can be inferred via the existential biconditional introduction rule.