At Mr. and Mrs. Hilbert's Hotel Infinity, the resident cat is puzzled. The hotel is fully booked -- the rooms are full of Numbers, both Odds and Evens -- yet guests continue to arrive. When Zero shows up, there's a massive room switching, and he stays, even though Mr. Hilbert insists he's not really a Number. Then the Letters appear and everyone still has a room, even though no Numbers have left. No matter how many guests arrive or depart, the hotel...