Related:

• The student is in the pudding as an exercise.
• The proof is left to the student as a pudding.
• The pudding is in the student. The student needs some exercise.
• Proof left as an exercise for your supervisor.
• 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....
• 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....
• An example is not proof.
• Lack of proof <> proof of lack.
• Conservativism: An exercise in futility.