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_7: P(x_7) -> S(x_7). forall x_7: P(x_7). forall x_7: S(x_7) -> P(x_7).
exists x_7: S(x_7) can be inferred via the existential modus ponens rule. exists x_7: P(x_7) <-> S(x_7) can be inferred via the existential biconditional introduction rule. exists x_7: S(x_7) <-> P(x_7) can be inferred via the existential biconditional introduction rule.