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_3: W(x_3) -> S_4(x_3). forall x_3: S_4(x_3) -> W(x_3). forall x_3: ~W(x_3).
forall x_3: ~S_4(x_3) can be inferred via the universal modus tollens rule. exists x_3: W(x_3) <-> S_4(x_3) can be inferred via the existential biconditional introduction rule. exists x_3: S_4(x_3) <-> W(x_3) can be inferred via the existential biconditional introduction rule.