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: forall z_4: P(z_4) -> S(z_4). exists z_4: S(z_4) -> P(z_4).
exists z_4: S(z_4) <-> P(z_4) can be inferred via the existential biconditional introduction rule. exists z_4: P(z_4) <-> S(z_4) can be inferred via the existential biconditional introduction rule.