Related:

• The exercise is proof of the student.
• The proof is left to the student as a pudding.
• Your supervisor is thinking about you.
• 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....
• You will have a long and unpleasant discussion with your supervisor.
• The solution of this problem is trivial and is left as an exercise for the reader.
• You get your exercise acting as a pallbearer for your friends who exercise
• Supervisor: someone with half your ability and 3 times your salary.