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: ~S(x_3). forall x_3: P(x_3) -> S(x_3). forall x_3: P(x_3) -> R(x_3). forall x_3: R(x_3) -> P(x_3).
exists x_3: ~P(x_3) can be inferred via the existential modus tollens rule. forall x_3: R(x_3) -> S(x_3) can be inferred via the universal transitivity rule. forall x_3: P(x_3) <-> R(x_3) can be inferred via the universal biconditional introduction rule. forall x_3: R(x_3) <-> P(x_3) can be inferred via the universal biconditional introduction rule.