Commentary on the Sixth Edition UNIX Operating System

"This directory contains a copy of John Lion's “A commentary on the Sixth Edition UNIX Operating System”. This form of the document is the one that Warren Toomey published on the USENET alt.folklore.computers newsgroup in May 1994. It's available in several forms."

http://www.lemis.com/grog/Documentation/Lions/

https://pdos.csail.mit.edu/6.828/2016/xv6.html