The answer to this riddle has a hole in the middle, And some have been known to fall in it. In tennis it's nothing, but it can be received, And sometimes a person may win it. Though not seen or heard it may be perceived, Like princes or bees it's in clover. The answer to this riddle has a hole in the middle, And without it one cannot start over.

The Mysterious Benedict Society and the Prisoner's Dilemma (ed. Chicken House, 2014) - ISBN: 9781909489271