"We could not study Unix versions that derive from the Research editions via AT&T System V, such as Solaris, AIX, and HPUX, because most of the corresponding code remains proprietary and inaccessible."<p>Understandable but disappointing. HPUX and AIX in particular are probably the closest thing to "living" UNIX time capsules.
Extremely interesting trend in cyclomatic complexity increasing then dropping in what looks like all systems and programs analyzed.<p>Interesting that Linux kernel is unusually low, about 4.5 while all the others (except gnu coreutils) are around 6.
Short explainer video for those who don’t want to read the whole thing:<p><a href="https://youtu.be/eCYkzciF28E" rel="nofollow">https://youtu.be/eCYkzciF28E</a>