THEM: i would like a book, a ball, and a hat.  YOU: i need one of either the book or ball and at least two hats  THEM: the book and the ball are not negotiable for me.  YOU: you have to give up one or there is no deal  THEM: i will only consider giving up the book but for all the hats.  YOU: one hat and one book for me, final offer  THEM: deal if i get the other two hats and the ball.