You know the jokes about "keep your books from before 2021"?
I just got a hard lesson. That is not a joke. Keep your 2021-era textbooks.
Someone asked me to have a look at some online learning materials, "Last Updated : 8 Apr, 2026" because something seemed wrong.
So I read it. The text does not parse as LLM output; there are no telling phrase structures, no em-dashes, no alerting idioms.
But the content? The actual thing to be learned?
It is coherent and completely wrong. The method and maths are right, but the intrinsic meanings of parameters are both completely plausible and utterly wrong.
It's like giving walking directions to someone in a car. Yes, the stairs to the beach are there, and they do get from the parking lot to the water. Yes, cars are things for going places. But if you try to do that - and you can! - you get a car submerging in the surf, not a 50kph-capable vehicle with no stoplights ahead.
And since there's no physically obvious problem, no car filling with water, just a number that does indicate things in other contexts but here is not linked to reality? Then decisions could get made, statements published, if nobody picks up on the extraordinary mis-use.
Keep your textbooks, especially anything with methods or maths!
