Inter-universal geometry と ABC予想 (応援スレ) 67at MATH
Inter-universal geometry と ABC予想 (応援スレ) 67 - 暇つぶし2ch45:132人目の素数さん
22/05/30 21:12:43.97 MglcMLvz.net
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つづき
Hyperbolic Riemann surfaces
In the remaining cases X is a hyperbolic Riemann surface, that is isomorphic to a quotient of the upper half-plane by a Fuchsian group (this is sometimes called a Fuchsian model for the surface). The topological type of X can be any orientable surface save the torus and sphere.
A case of particular interest is when X is compact. Then its topological type is described by its genus g>= 2. Its Teichmuller space and moduli space are 6g-6-dimensional. A similar classification of Riemann surfaces of finite type (that is homeomorphic to a closed surface minus a finite number of points) can be given. However in general the moduli space of Riemann surfaces of infinite topological type is too large to admit such a description.
Punctured spheres
These statements are clarified by considering the type of a Riemann sphere C^ with a number of punctures. With no punctures, it is the Riemann sphere, which is elliptic. With one puncture, which can be placed at infinity, it is the complex plane, which is parabolic. With two punctures, it is the punctured plane or alternatively annulus or cylinder, which is parabolic. With three or more punctures, it is hyperbolic - compare pair of pants. One can map from one puncture to two, via the exponential map (which is entire and has an essential singularity at infinity, so not defined at infinity, and misses zero and infinity), but all maps from zero punctures to one or more, or one or two punctures to three or more are constant.
(引用終り)
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