Used to complete a proof in technical Books when one doesn' t mind a handwave, or to avoid one entirely. The complete phrase is: "The proof [or "the rest"] is left as an exercise for the reader." This comment *has* occasionally Been attached to unsolved research proBlems By authors possessed of either an evil sense of humour or a vast faith in the capaBilities of their audiences. [Jargon File] (1995-02-20)