Paper 3, Section II, D

Algebra and Geometry
Part IA, 2007

In the group of Möbius maps, what is the order of the Möbius map z1zz \mapsto \frac{1}{z} ? What is the order of the Möbius map z11zz \mapsto \frac{1}{1-z} ?

Prove that every Möbius map is conjugate either to a map of the form zμzz \mapsto \mu z (some μC\mu \in \mathbb{C} ) or to the mapzz+1\operatorname{map} z \mapsto z+1. Is zz+1z \mapsto z+1 conjugate to a map of the form zμz?z \mapsto \mu z ?

Let ff be a Möbius map of order nn, for some positive integer nn. Under the action on C{}\mathbb{C} \cup\{\infty\} of the group generated by ff, what are the various sizes of the orbits? Justify your answer.