Gardner-Denver is the largest manufacturer of ratchet wrenches and their replacement parts in the United States. Gardner-Denver had two different lists of prices for its wrenches and parts. Its blue list had parts that, if purchased in quantities of five or more, were available for substantially less than its white list prices. Did Gardner-Denver engage in price discrimination with its two price lists? [D. E. Rogers Assoc., Inc. v Gardner-Denver Co., 718 F2d 1431 (6th Cir)]