Q. Each seller has two types of goods; good A and good B. You and or three sellers can set your price for good A, price for good B and price for bundle that consists of goods A + B. Notice that ways and computer interface are colour coded and make use of fact that yellow and blue make green. You do not incur any cost to produce goods you sell and thus your profit equals selling price if you make a sell. Or three sellers do not have any costs either. If I am selling, who is buying?