THEM: i'd like the book and 1 hat.  YOU: i will give you three balls  THEM: balls are 0 for me.  YOU: how about one hat?  THEM: i can do both hats or 1 book and 1 hat.  YOU: how about one of each?  THEM: balls are 0 for me.  YOU: well the best i can do is give you two hats and one ball  THEM: i just want the two hats. balls are 0 for me.  YOU: i can only spare one hat  THEM: you just offered 2 hats.  YOU: so you want just two hats?