THEM: i would like the ball and hat  YOU: i can't give up the ball and the hat. how about i get the ball and 2 books.  THEM: do you need the books?  YOU: not if i can have the ball and the hat.  THEM: i dont want them at all  YOU: well i can't just take the books.  THEM: ill take 1 book 1 ball  YOU: okay that will have to work.