The holomorphic structure sheaf #
The holomorphic structure sheaf of a complex manifold assigns to an open set U the ring
of complex analytic maps U → ℂ. Its sections are Mathlib's ContMDiffMap at regularity
ω, so their pointwise ring and complex vector space structures are reused directly.
The same restriction maps give a sheaf of complex vector spaces, suitable for cohomology.
On a complex curve, these sections are precisely the manifold-differentiable functions.
On a compact connected complex manifold, the constant-section map is an algebra
isomorphism ℂ ≃ₐ[ℂ] H⁰(X, 𝒪). The inverse is evaluation at any point, independently of
which point is chosen. In particular, the space of global sections has dimension one.
The function coercions and algebra instance use the bundled analytic-map representation.
Pointwise computation is provided by section evaluation lemmas.
The sheaf of modules has exactly the same underlying presheaf of functions.
Evaluation of germs gives a surjective ring homomorphism from each stalk to ℂ.
Holomorphic maps induce morphisms to the pushed-forward structure sheaf by precomposition,
and pull back holomorphic germs (stalkPrecomp), functorially and preserving their values.
The sheaf construction follows smoothSheafCommRing in
Mathlib/Geometry/Manifold/Sheaf/Smooth.lean by Heather Macbeth and Adam Topaz, using
StructureGroupoid.LocalInvariantProp.sheaf at analytic rather than smooth regularity.
The stalk evaluation and precomposition constructions follow smoothSheafCommRing.evalHom
and ContMDiff.smoothSheafCommRingHom in the same file.
The global-sections computation uses Mathlib's
MDifferentiable.exists_eq_const_of_compactSpace (the maximum principle).
For the classical structure sheaf and its global sections, see Otto Forster,
Lectures on Riemann Surfaces, §§1, 6.
The holomorphic structure sheaf of a complex manifold, as a sheaf of commutative rings.
Its sections on U are the complex analytic maps U → ℂ.
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Sections of the structure sheaf are bundled complex analytic functions.
The function underlying a section of the structure sheaf.
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Sections of the structure sheaf are equal if they agree at every point.
A section of the structure sheaf is complex analytic on its domain.
A section of the structure sheaf is holomorphic on its domain.
Complex analytic functions give sections of the structure sheaf for any complex model.
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Holomorphic functions on a complex curve give sections of its structure sheaf.
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Evaluation of germs at their base point, as a morphism of commutative rings.
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The ring homomorphism evaluating a holomorphic germ at its base point.
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Evaluation after the germ map is evaluation on the original section.
Evaluation after the germ map is evaluation on the original section.
Evaluation of a germ, in the categorical form of the stalk evaluation map.
Evaluating the germ of a section returns its value at the base point.
Every complex number is the value of a constant holomorphic germ.
Precomposition by a complex analytic map, on the rings of holomorphic sections.
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A complex analytic map induces a morphism 𝒪_Y ⟶ f_*𝒪_X by precomposition.
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A holomorphic map between complex curves induces a morphism of structure sheaves.
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A complex analytic map f pulls holomorphic germs at f x back to holomorphic germs at x,
by precomposition: the stalk map of homOfContMDiff.
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The pullback of the germ of a section is the germ of the precomposed section.
Pulling a germ back along f preserves its value: the value at x of the pullback is the
value at f x of the germ.
Pulling germs back along the identity does nothing.
Pulling germs back along g ∘ f is pulling back along g and then along f.
The holomorphic structure sheaf viewed as a sheaf of complex vector spaces.
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Sections of the module sheaf are the same complex vector spaces as the ring sections.
Ring sections and module sections have the same complex vector space structure.
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A section of the module sheaf is complex analytic on its domain.
A section of the module sheaf is holomorphic on its domain.
Complex analytic functions give sections of the module sheaf for any complex model.
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Sections of the module sheaf are equal if they agree at every point.
Forgetting the ring or module structure gives the same presheaf of functions.
On a nonempty compact connected complex manifold, every global holomorphic section is a unique constant section.
Constants identify the global sections of the holomorphic structure sheaf with ℂ.
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Evaluation at any point is the inverse of the constant-section isomorphism.
The space of global holomorphic sections on a nonempty compact connected complex
manifold is one-dimensional over ℂ.
The module sheaf's global sections on a nonempty compact connected complex manifold form a one-dimensional complex vector space.