by Ivar Ekeland (2006). Incredibly imaginative, and beautifully illustrated (by John O’Brien), short “children’s” book about the mathematician Georg Cantor’s ideas of infinity and David Hilbert’s rendition of these difficult ideas in terms of a hotel with infinitely many rooms. In a playful manner, the book illustrates that even though all rooms are occupied by a guest, the hotel can always accommodate twice the number of guests, one of many strange properties of infinity. It can even host all fractions but not all decimals. A true gem!