11. Proposition 2.6.4

Let $f \in M ö b (C)$ , and denote $w_{1} = f (0)$ , $w_{2} = f (1)$ , and $w_{3} = f (\infty)$ . Then $f (z) = w$ satisfies the following relation:
:?:

\frac{w - w_{1}}{w_{1} - w_{2}} \frac{w_{2} - w_{3}}{w_{3} - w} = z