Gardner-Denver, the largest manufacturer of ratchet wrenches and their replacement parts in the United States, has a dual pricing system for wrench parts and components. Its blue list had parts that, if purchased in quantities of five or more, were available for substantially less than its white list prices. Has Gardner-Denver engaged in price discrimination with its two price lists? [D. E. Rogers Assoc., Inc. v Gardner-Denver Co., 718 F.2d 1431 (6th Cir. 1983)]