fix wording

Author: vladak

history.tex

@@ -112,7 +112,7 @@
 moment in the history of this system} $\Rightarrow$ it was much easier to port
 UNIX to different architectures.
 \item The legendary book \emph{A commentary on the Unix
-Operating System} by John Lions was found on version 6.
+Operating System} by John Lions was based on version 6.
 \item Microsoft did not sell XENIX directly, it was licensed to OEM companies
 (Original Equipment Manufacturer) such as Intel, SCO a others. Other companies
 then ported XENIX to 286 (Intel) and 386 (SCO, 1987). It is possible to find