If the “take a book, leave a book” sign — found in a very high-end, East Coast retirement community — was to be believed, the number of books on that table should always be the same. But that was not the case. I’ve been visiting a relative there for years and it seems like the number of books has grown substantially.When I say a “high-end retirement community,” I don’t mean simply expensive. The residents include former chancellors of Ivy League…