At one point I a friend was mentioning the regex golf https://xkcd.com/1313/ comic and how some insane person on the internet solved it. I mentioned my pains with the regex bit of the Design of Computer Programs course, and how Norvig had some Chtulhu like ability to write regexes that befuddle mortal minds. Lo and behold, it had been Norvig all along solving that. Python notebook available in the pytudes above.