A Zen teaching riddle. Classically, koans are attractive paradoxes to be meditated on; their purpose is to help one to enlightenment by temporarily jamming normal cognitive processing so that something more interesting can happen (this practice is associated with Rinzai Zen Buddhism). Defined here because hackers are very fond of the koan form and compose their own koans for humorous and/or enlightening effect. See Some AI Koans, has the X nature, hacker humor.