- make a backup copy of the folder we created 
 - run: git log   # get the sha
 - run: gitk
 - run: git checkout "the sha"
 - edit: paper.tex (see that old version) (and KEEP your editor open)
 -- change: intro to something shorter
 -- change: some other part to something shorter
 - run: git commit
 - run: gitk (just init + this)
 - run: gitk --all (all named, not this) (also works with "git log --all")
 - run: git checkout -b shorter
 - run: gitk --all (notice the bold, "git log --graph --oneline  --decorate"g)

 - run: git checkout master
    - when you do that, your open editor should tell
     you that the file changed, right away or when
     you try to change edit the file. If it does not
     change your editor for something better/safer.
 - run: gitk --all (it is bold that moved)
 - run: git merge shorter (no conflicts)
 - run: gitk --all

 - run: git checkout master # already on it
 - run: git checkout -b pig
 - add the pig image
 - edit:
 -- change the title
 -- replace the bird with a pig
 - commit it

 - run: git checkout master
 - edit:
 -- go from one bird to 3 birds
\includegraphics[width=2.5cm]{a_bird.png}
\includegraphics[width=3cm]{a_bird.png}
\includegraphics[width=2cm]{a_bird.png}
 -- modify something else
 - commit
 - run: gitk --all

 - run: git merge pig (conflict)
 - run: git status
 - run: git gui    (to have a look)
 - run: gitk --all (in progress)
 - run: git merge --abort (back to normal)
 - run: git merge pig (again)
 - open and fix (look at title, modif part and the conflict)
 - run: pdflatex paper.tex
 - run: git status
 - run: git add paper.tex
 - run: git commit