THEM: i'd like 2 hats, 1 book and 1 ball please.  YOU: i need 2 books and 1 hat or 2 hats and 1 book.  THEM: i can give you 2 books, but not 2 hats. how about 2 books and 2 balls, no hat?  YOU: deal.  THEM: deal. confirming you get 2 books, and 2 balls and i get all the hats.