this makes a lot more sense alongside the actual souce code, like in this version:

https://www.amazon.com/Lions-Commentary-Unix-John/dp/1573980...

I had a colleague who did some work on PDP-11 on his early career. Excited, I asked "So you were using C (language) there?" "No, it's too early" He told me, kind of dismissively. In retrospect it was obvious - The PDP11-based Unix of the Lion's Book [1] was what I had in my mind, but that was probably more like an academic pursuit than a foundational OS of commercial software.

[1] https://www.amazon.com/Lions-Commentary-Unix-John/dp/1573980...