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: P_9(a_9). forall x_9: S(x_9) <-> P_4(x_9). forall x_9: P_4(x_9) -> ~P_9(x_9).
exists x: P_9(x) can be inferred via the existential generalization rule. forall x_9: S(x_9) -> P_4(x_9) can be inferred via the universal biconditional elimination rule. forall x_9: P_4(x_9) -> S(x_9) can be inferred via the universal biconditional elimination rule.