This article originally appeared in The Games Cafe, a now defunct web site devoted to lovers of board games and puzzles. In the article I occasionally refer to other Games Cafe article. I decided to leave these references as is, even though they no longer link to anything.

Part 1 of the definition says that puzzles are a form of play. Part 2 distinguishes puzzles from other forms of plays, such as games and toys. This deceptively simple definition has some interesting consequences. For instance, here’s the first puzzle I invented. (Martin Gardner first wrote about it in Games Magazine.) The figure below is a letter of the alphabet that has been cut of paper and folded just once. It is not the letter L. What letter is it?