You might have heard the story about the author of a calculus textbook that made so much money he could afford to build a mansion in the shape of an integral symbol.

Well, his name was James Stewart and he died last December, so now Integral House is up for sale, for $23m.

Yes, textbooks are that ridiculously expensive in North America.

The Daily Beast has written an article about the sale, and there’s a good thread on MetaFilter with a mix of discussion about the house itself and lots of griping about the American textbook racket.