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 x_9: S_4(x_9). forall x_9: P_8(x_9) <-> Q_8(x_9). forall x_9: S_4(x_9) -> Q_8(x_9). exists x_9: W(x_9) -> P_8(x_9).
forall x_9: Q_8(x_9) can be inferred via the universal modus ponens rule. forall x_9: P_8(x_9) -> Q_8(x_9) can be inferred via the universal biconditional elimination rule. forall x_9: Q_8(x_9) -> P_8(x_9) can be inferred via the universal biconditional elimination rule.