F x a b

F x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a bF x a b