Gluing morphisms of locally ringed spaces along an open cover #
Morphisms of locally ringed spaces g i : X | Uᵢ → W defined on the members of an open cover of
X and agreeing on the overlaps X | (Uᵢ ⊓ Uⱼ) glue to a morphism X → W restricting to the
g i — the existence half of the locality of morphisms (Hironaka/AnalyticSpace/HomLocal.lean is
the uniqueness half). Hironaka's universal mapping property (**) of a monoidal transformation
[Hir64, Ch. 0, §2] needs it: the lift of a test pair (Y', f') into the blow-up is constructed on
the members of an open cover of Y' (over the complement of the centre and in each blow-up
chart) and glued; the pieces agree on the overlaps by uniqueness. Elementary sheaf theory, not in
the sources; stated for general locally ringed spaces.
restrictIncl X h : X | V → X | Wfor nested opensV ≤ W— the inclusion of subtypes with the restriction of sections along the inclusion of image opens as sheaf component, so that its sheaf component is a restriction map of𝒪_XandrestrictIncl ≫ ofRestrict W = ofRestrict V. Compatibility of the pieces is stated with it:GlueCompatible U gsaysrestrictIncl ≫ g i = restrictIncl ≫ g jonX | (Uᵢ ⊓ Uⱼ).- The base map is pasted from the bases of the pieces (
ContinuousMap.liftCover). - A section
sof𝒪_WoverVpulls back to the pieces(g i)^* sover the image opensgluePieceOpens i V = Uᵢ ∩ b⁻¹ V; they are compatible because their germs agree, through the overlap space, when the pieces do (germ_gluePieceSection_of_overlap,gluePieceSection_isCompatible), and glue uniquely (TopCat.Sheaf.existsUnique_gluing') toglueSection V s; the glued sections form a ring homomorphism and a natural transformation by the uniqueness of the gluing. - The stalk map of the glued morphism at
x ∈ Uᵢis the stalk map ofg i, read through the identification of the image points and the stalk of the open subspace (glueHom_stalkMap), hence local;ofRestrict ≫ glueOfCover = g ibySheafedSpace.hom_stalk_ext. - The
K-morphism form (KLocallyRingedSpace.glueOfCover): the glued morphism respects theK-structures because its global sections restrict to those of the pieces.
Mathlib has LocallyRingedSpace.GlueData (gluing spaces), IsOpenImmersion.lift and the
sheaf-level existsUnique_gluing', but no gluing of morphisms out of a space covered by opens;
Scheme.OpenCover.glueMorphisms is for schemes.
The inclusion X | V → X | W of the restrictions to nested opens V ≤ W, as a morphism of
presheafed spaces: the inclusion of subtypes on points, restriction of sections along the inclusion
of image opens on sheaves.
Equations
- One or more equations did not get rendered due to their size.
Instances For
X | V → X | W → X is X | V → X.
The stalk map of the inclusion X | V → X | W is an isomorphism (the two ofRestrict stalk
maps are).
The inclusion X | V → X | W of the restrictions to nested opens V ≤ W, as a morphism of
locally ringed spaces.
Equations
- AnalyticSpace.restrictIncl X h = { toHom := AnalyticSpace.restrictInclHom X h, prop := ⋯ }
Instances For
The pieces g i : X | Uᵢ → W agree on the overlaps X | (Uᵢ ⊓ Uⱼ).
Equations
- One or more equations did not get rendered due to their size.
Instances For
The members of the cover are neighbourhoods of every point.
The glued base map: x ↦ (g i).base x for any i with x ∈ Uᵢ.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The image in X of (g i).base ⁻¹ V ⊆ Uᵢ: the open on which the piece (g i)^* s lives.
Equations
- AnalyticSpace.gluePieceOpens U g i V = ⋯.functor.obj ((TopologicalSpace.Opens.map (g i).base).obj V)
Instances For
The piece (g i)^* s, a section of X over gluePieceOpens i V.
Equations
- AnalyticSpace.gluePieceSection U g i V s = (CategoryTheory.ConcreteCategory.hom ((g i).c.app (Opposite.op V))) s
Instances For
The germ of a piece at a point, through the overlap space X | (Uᵢ ⊓ Uⱼ): the piece of g k
restricted along X | (Uᵢ ⊓ Uⱼ) → X | U_k has the germ of the piece itself.
The pieces (g i)^* s are compatible on the overlaps (their germs agree, through the overlap
space, because the pieces agree there).
The glued section over b⁻¹ V, b the glued base map: the unique section restricting to the
piece (g i)^* s on every gluePieceOpens i V.
Equations
- AnalyticSpace.glueSection U g hU hg V s = Exists.choose ⋯
Instances For
The glued sections form a ring homomorphism 𝒪_W(V) → 𝒪_X(b⁻¹ V).
Equations
- AnalyticSpace.glueSectionHom U g hU hg V = CommRingCat.ofHom { toFun := AnalyticSpace.glueSection U g hU hg V, map_one' := ⋯, map_mul' := ⋯, map_zero' := ⋯, map_add' := ⋯ }
Instances For
The sheaf component of the glued morphism.
Equations
- AnalyticSpace.glueCoverC U g hU hg = { app := fun (V : (TopologicalSpace.Opens ↑↑W.toPresheafedSpace)ᵒᵖ) => AnalyticSpace.glueSectionHom U g hU hg (Opposite.unop V), naturality := ⋯ }
Instances For
The glued morphism of presheafed spaces.
Equations
- AnalyticSpace.glueHom U g hU hg = { base := AnalyticSpace.glueCoverBase U g hU hg, c := AnalyticSpace.glueCoverC U g hU hg }
Instances For
The stalk map of the glued morphism at a point of Uᵢ is the stalk map of g i, read through
the identification of the image points and the stalk of the open subspace.
The morphism of locally ringed spaces glued from compatible pieces g i : X | Uᵢ → W
along an open cover of X.
Equations
- AnalyticSpace.glueOfCover U g hU hg = { toHom := AnalyticSpace.glueHom U g hU hg, prop := ⋯ }
Instances For
The glued morphism restricts to the pieces.
The inclusion X | V → X | W of the open subspaces of nested opens V ≤ W, as a K-morphism
(the factorization of X | V → X through X | W → X).
Equations
Instances For
The K-morphisms g i : X | Uᵢ → W agree on the overlaps X | (Uᵢ ⊓ Uⱼ).
Equations
- One or more equations did not get rendered due to their size.
Instances For
The K-morphism glued from compatible K-morphisms g i : X | Uᵢ → W along an open cover of
X: the glued morphism of locally ringed spaces, which respects the K-structures because its
global sections restrict to those of the pieces.
Equations
- AnalyticSpace.KLocallyRingedSpace.glueOfCover U g hU hg = ⟨AnalyticSpace.glueOfCover U (fun (i : ι) => ↑(g i)) hU ⋯, ⋯⟩