A certain credit-card company awards its customers bonus points for using its credit card  Customers can use accumulated points in the purchase of brand name merchandise by mail at prices lower than the manufacturers' suggested retail prices
At any given time, ttherefore, customers who purchase merchandise using the bonus points spend less than they would spend if they purchased the same merchandise in retail stores
The bonus points cannot be used by the creditcard customers in the purchase of brand name merchandise that is not available for purchase in retail stones.