THEM: i can offer you two books  YOU: i'll take two books and the ball.  THEM: how about i give you all the books and i take the rest  YOU: oooo. no can do. i can give you both hats.  THEM: ill take the basketball and one hat how about that?  YOU: can't give up the ball. i can give up the hats and a book.  THEM: ill give you the basketball for everything else.