Robin J Wilson's book is "not", as he assures the reader in the Preface, "a history of mathematics book in the conventional sense of the word". No indeed. It is, rather, a selective account of aspects of the history of mathematics which have appeared on postage stamps from across the world.
This is a game played between a team of 3 people (Ann, Bob and Chris, say), and a TV game show host. The team enters the room, and the host places a hat on each of their heads. Each hat is either red or blue at random (the host tosses a coin for each team-member to decide which colour of hat to give them). The players can see each others' hats, but no-one can see their own hat.