“If video games had been around in 350 BC, Euclid would have made a video game,”Devlin told me. The thirteen books of Euclid’s Elements would have been the supplemental material, a PDF file that you could read if you wanted to. “People think I’m joking—I absolutely mean that. Euclid would not have written a textbook, he would have designed a video game.” Peek at any of his proofs, Devlin said, and you’ll quickly find that the great Greek mathematician, often called the father of geometry, is asking the reader to do things. “He says, ‘Draw this arc,’ ‘Drop this perpendicular.’ ‘Bisect that line.’ These are actions, and actions are what you get in video games.”