Note that sources are available.

comprehensive-gpl-guide.tex

@@ -73,6 +73,8 @@ it is not allowed.''.  However, those who seek to make modified versions of
 those licenses should note the
 \href{https://www.gnu.org/licenses/gpl-faq.html#ModifyGPL}{explanation given in the GPL FAQ}.
 
+Patches are welcome to this material.  Sources can be found in the Git
+repository at: \url{https://gitorious.org/gpl-compliance-tools/tutorial/}
 }
 \end{center}