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.
(1995-02-20)
Try this search on Wikipedia, OneLook, Google
Nearby terms: execution « executive « Executive Systems Programming Oriented Language « exercise, left as an » exhaustive testing » existential quantifier » exit