Ask HN: What article said 7 last Unix code someone could keep in their head?

I'm looking for an article/paper I found on HackerNews (maybe in 2018 or 2019) that someone posted that was some description of a UNIX version (7 I think?) and in the introduction they mentioned it being the last version of UNIX that was small enough for one person to keep all the code in their head.

Does anyone know what paper I might be thinking of? I can't seem to locate it.