Fix \abs command

git-svn-id: svn+ssh://kasztan.ifj.edu.pl/home/theory/svnroot/camtoph/Gituliar@22 d7a11de1-dac9-4f50-91c3-d62249753022
Finish general derivation of \Gamma^2

git-svn-id: svn+ssh://kasztan.ifj.edu.pl/home/theory/svnroot/camtoph/Gituliar@23 d7a11de1-dac9-4f50-91c3-d62249753022
Merge branch 'master' of github.com:gituliar/physics