= E =
exercise, left as an adj.
[from technical books] Used to
complete a proof 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 humor or a vast faith in the
capabilities of their audiences.
--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.