1. it must involve an evil, an unpleasantness to the victim;
2. it must be for an offence, actual or supposed;
3. it must be of an offender, actual or supposed;
4. it must be the work of personal agencies;
5. it must be imposed by authority conferred through or by the insti¬tutions against the rules of which the offence has been committed.
A sixth criterion . . . is that the pain or unpleasantness should be an essential part of what is intended and not merely a coincidental or accidental outcome.