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_18: P_18(x_18) -> Q_18(x_18). forall x_18: Q_18(x_18). forall x_18: Q_18(x_18) -> P_18(x_18).
forall x_18: P_18(x_18) can be inferred via the universal modus ponens rule. forall x_18: P_18(x_18) <-> Q_18(x_18) can be inferred via the universal biconditional introduction rule. forall x_18: Q_18(x_18) <-> P_18(x_18) can be inferred via the universal biconditional introduction rule.