THEM: i would like the ball and 2 hats please. you can have the book and 2 hats.  YOU: i really need the ball. would you take all the hats and i get the ball and the book?  THEM: i have to have the ball. you can have 3 of the hats and the book.  YOU: hats are worthless to me. i can only make a deal if i get the ball. how about i give you everything except the ball?  THEM: okay deal.