Version 6.0. From this version (edition) forward both volumes have the same version number.
This is a major update, many changes, although most of the changes are minor. Altogether 24 new figures and a few new exercises. New font hopefully making the PDF more readable, plus get rid of some shortcuts that seemed to have been confusing to students.
See https://www.jirka.org/ra/ for more information on what's changed, namely
https://www.jirka.org/ra/changes.html - changes to Volume I
https://www.jirka.org/ra/changes2.html - changes to Volume II