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_4: S(x_4) -> ~Q_4(x_4). forall x_4: S(x_4) -> Q_1(x_4). forall x_4: Q_4(x_4). forall x_4: Q_1(x_4) -> S(x_4).
exists x_4: ~S(x_4) can be inferred via the existential modus tollens rule. forall x_4: S(x_4) <-> Q_1(x_4) can be inferred via the universal biconditional introduction rule. forall x_4: Q_1(x_4) <-> S(x_4) can be inferred via the universal biconditional introduction rule.