Paper 1, Section II, F

Riemann Surfaces | Part II, 2018

Given a complete analytic function F\mathcal{F} on a domain GCG \subset \mathbb{C}, define the germ of a function element (f,D)(f, D) of F\mathcal{F} at zDz \in D. Let G\mathcal{G} be the set of all germs of function elements in GG. Describe without proofs the topology and complex structure on G\mathcal{G} and the natural covering map π:GG\pi: \mathcal{G} \rightarrow G. Prove that the evaluation map E:GC\mathcal{E}: \mathcal{G} \rightarrow \mathbb{C} defined by

E([f]z)=f(z)\mathcal{E}\left([f]_{z}\right)=f(z)

is analytic on each component of G\mathcal{G}.

Suppose f:RSf: R \rightarrow S is an analytic map of compact Riemann surfaces with BSB \subset S the set of branch points. Show that f:R\f1(B)S\Bf: R \backslash f^{-1}(B) \rightarrow S \backslash B is a regular covering map.

Given PS\BP \in S \backslash B, explain how any closed curve in S\BS \backslash B with initial and final points PP yields a permutation of the set f1(P)f^{-1}(P). Show that the group HH obtained from all such closed curves is a transitive subgroup of the group of permutations of f1(P)f^{-1}(P).

Find the group HH for the analytic map f:CCf: \mathbb{C}_{\infty} \rightarrow \mathbb{C}_{\infty} where f(z)=z2+z2f(z)=z^{2}+z^{-2}.

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