Cats and Numbers!

Maryn! Are you listening to me? If the Port Moody Kids Library is not currently featuring this book as the greatest kids' math book EVER, it has to start doing so.

Seriously, this book is the most adorable little thing I have read in ages, and uses a cute story about a puzzled cat (and justifiably so) to explain some of the basic concepts of infinite set theory. I am so filled with nerd love for it right now that I can hardly speak. (Or that's because of the germs ravaging my lungs, but nevermind.) This could clearly be, for some future set theorist, the tipping point into higher mathematics that Rocky's Boots was for me in logic. (I honestly never knew I was learning to build logic gates from computer science - I just wanted to make the raccoon do a nifty dance.)

The story is actually a standard metaphor from set theory, called Hilbert's Hotel, in which there are infinitely many guests (in this case, the Numbers), and more show up who need rooms of their own. But if all the rooms are full, how can you let in more guests? It helps when your hotel is infinite! In mathier terms, the story shows how you can establish a one-to-one correspondence between different infinite sets, showing that (by set-theoretic standards), they're the same size (cardinality). And it shows this by little stories about how the guests have to change rooms when new ones show up, and they have to do all sorts of clever things to make sure everyone gets a room.

Also, Mr. Hilbert, who runs the hotel in this story, is drawn to look like one of my favourite pictures of David Hilbert, the mathematician, and basically, it's all-around wonderfulness and math love.