Modify the "Analysis of model 1" chapter.

Clearify how the coupling and decoupling constraints
differ from the other constraints.
Also did some small text- and formulas- fixes.
Modify the "Model 2" chapter.

Remake of the chapter to make it more clear. The term
"path" was replaced by "position" and the chapter was
divided into smaller sections.
Small fixes with text and with graph colors.