**J.C. Álvarez Paiva**

In this chapter we study the action of the projective group on the real projective line.

- Anything preceded by a * may be left for a second reading.
- Next to the exercises there is a two-digit number in parentheses which describes its degree of difficulty. The simplest exercises are identified by a (00), while the hardest -- those that could take you a week of intensive brain work -- are identified by a (50).

- Basic definitions
- The fundamental theorems
- Harmonic quadruples and von Staudt's theorem
- Bibliography
- About this document ...

Juan Carlos Alvarez 2000-10-27