nLab sheaf of meromorphic functions

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Contents

Context

Topos Theory

topos theory

Background

Toposes

Internal Logic

Topos morphisms

Extra stuff, structure, properties

Cohomology and homotopy

In higher category theory

Theorems

Contents

Definition

Let (X,𝒪 X)(X, \mathcal{O}_X) be a ringed space. Consider the subsheaf of sets 𝒮𝒪 X\mathcal{S} \subset \mathcal{O}_X of the structure sheaf such that for each open subset UXU \subset X, Γ(U,𝒮)\Gamma(U, \mathcal{S}) consists of only the regular sections of 𝒪 X\mathcal{O}_X over UU, i.e. those elements sΓ(U,𝒪 X)s\in\Gamma(U, \mathcal{O}_X) for which s| Vf=0s|_V f=0 implies f=0f=0 for all fΓ(V,𝒪 X)f\in\Gamma(V,\mathcal{O}_X) for all opens VXV\subseteq X. Consider the presheaf of rings on XX

UΓ(U,𝒪 X)[Γ(U,𝒮) 1] U \quad\mapsto\quad \Gamma(U, \mathcal{O}_X)[\Gamma(U, \mathcal{S})^{-1}]

which assigns to UU the ring of fractions of Γ(U,𝒪 X)\Gamma(U, \mathcal{O}_X) with denominators in Γ(U,𝒮)\Gamma(U, \mathcal{S}); its sheafification X\mathcal{M}_X is called the sheaf of (germs of) meromorphic functions on XX. The sections of X\mathcal{M}_X over XX are called the meromorphic functions on X and we denote this ring M(X)=Γ(X, X)M(X) = \Gamma(X, \mathcal{M}_X).

Properties

Proposition

For every open subset UXU \subset X there is a canonical isomorphism between U\mathcal{M}_U and the restriction of X\mathcal{M}_X to UU.

Proposition

For every point xXx \in X there is a canonical isomorphism between the stalk X,x\mathcal{M}_{X,x} and 𝒪 X,x[𝒮 x 1]\mathcal{O}_{X,x}[\mathcal{S}_x^{-1}].

References

Last revised on September 12, 2021 at 14:06:51. See the history of this page for a list of all contributions to it.