Exercise, Left as an
/ek-sər-ˌsīz left əz ən/
[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.
