The professor wasn't perfect. As has been pointed out above, the last lecture did indeed contain a lie. "On the days when nobody caught the lie, we all sat in

The professor wasn't perfect. As has been pointed out above, the last lecture did indeed contain a lie. "On the days when nobody caught the lie, we all sat in silence, looking at each other as Dr. K, looking quite pleased with himself, said with a sly grin: “Ah ha! Each of you has one falsehood in your lecture notes. Discuss amongst yourselves what it might be, and I will tell you next Monday. That is all.”" If, as the article said, he repeated this message as usual at the end of the lecture, it was a lie. (Unless, of course, the students all wrote down his oft-repeated message in their lecture notes - which I find unlikely.)