- Fixed the grammar in 2.2.4.5, which was missing a unary -> factor production
- Improved explanation for the proof in 2.2.5
Added a formal proof on 2.2.5 2
Improved formatting on 2.2.5.2
Fixed small typo on the roman numerals exercise.
Merge pull request #22 from filipegoncalves/master

Formal proof on exercise 2.2.5.2