Related:

• exercise, left as an: [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....
• Proof left as an exercise for your supervisor.
• The solution of this problem is trivial and is left as an exercise for the reader.
• NP- /N-P/ pref. Extremely. Used to modify adjectives describing a level or quality of difficulty
  he connotation is often `more so than it should be' This is generalized from the computer-science terms `NP-hard' and `NP-complete'...
• The exercise is proof of the student.
• Feminizts are proof that God has a sense of humor.
• QOTD: "This is a one line proof... if we start sufficiently far to the left.
• The proof is left to the student as a pudding.
• How many mathematicians -- does it take to screw in a light bulb?
  None. It's left to the reader as an exercise....