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_18: P_11(x_18) or P_12(x_18). forall x_18: P_12(x_18) -> P_18(x_18). forall x_18: P_11(x_18) -> U(x_18). forall x_18: P_18(x_18) <-> U(x_18). forall x_18: S(x_18).
forall x_18: P_18(x_18) -> U(x_18) can be inferred via the universal biconditional elimination rule. forall x_18: U(x_18) -> P_18(x_18) can be inferred via the universal biconditional elimination rule.