Note missing content
Add last part of the problem 3 (GH-10)
Add missing part
Get bibliography to work on my machine

One could include `central-bibtex` as a submodule.
Replace p
Merge new header
Write more, correct errors
Add some notes for problem 2 (GH-9)
Assign more structure to GH-8
Fix grammar error
Add even more structure
Remove line
Add some more environments
Add some warnings
Add proof of other relation
More text
Work on GH-9