Module

LocalRepresenterGluing.lean

Nyll.EtaleCohomology.Constructible.LocalRepresenterGluing
6 declarations indexed from sourceView source ↗

Gluing finite étale local representers on a directed open cover

The actual representing equivalences on the small étale sites determine all transition maps and their cartesian squares. Relative gluing then constructs a finite étale scheme on the whole base, whose restrictions are the chosen local schemes. No gluing comparisons or cocycle laws are assumed.

Imports13
Imported by3

Declarations

EtaleCohomology.etaleOpenCoverDiagram

Regard the directed open cover as a diagram in the base's small étale category.

Source context 5 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open AlgebraicGeometry CategoryTheory Limits SchemeTheory.WeilRestriction
universe u v
namespace EtaleCohomology
variable {X : Scheme.{u}} (G : Sheaf X.smallEtaleTopology (Type u))
  (𝒰 : X.OpenCover) [Category.{v} 𝒰.I₀] [𝒰.LocallyDirected]
def etaleOpenCoverDiagram : 𝒰.I₀ ⥤ X.Etale
EtaleCohomology.etaleLocalRepresenterGluingData

Ordinary local representations give actual relative gluing data via the slice equivalences of the small étale category.

Source context 6 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open AlgebraicGeometry CategoryTheory Limits SchemeTheory.WeilRestriction
universe u v
namespace EtaleCohomology
variable {X : Scheme.{u}} (G : Sheaf X.smallEtaleTopology (Type u))
  (𝒰 : X.OpenCover) [Category.{v} 𝒰.I₀] [𝒰.LocallyDirected]
variable (W : ∀ i : 𝒰.I₀, FiniteEtale (𝒰.X i))
  (h : ∀ i : 𝒰.I₀, ((etalePostcompose (𝒰.f i)).op ⋙ G.obj).RepresentableBy
    ((finiteEtaleToEtale (𝒰.X i)).obj (W i)))
def etaleLocalRepresenterGluingData : 𝒰.RelativeGluingData
EtaleCohomology.etaleLocalRepresenterGluingData_app

The local structural maps of the gluing data are the original finite étale maps.

Source context 6 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open AlgebraicGeometry CategoryTheory Limits SchemeTheory.WeilRestriction
universe u v
namespace EtaleCohomology
variable {X : Scheme.{u}} (G : Sheaf X.smallEtaleTopology (Type u))
  (𝒰 : X.OpenCover) [Category.{v} 𝒰.I₀] [𝒰.LocallyDirected]
variable (W : ∀ i : 𝒰.I₀, FiniteEtale (𝒰.X i))
  (h : ∀ i : 𝒰.I₀, ((etalePostcompose (𝒰.f i)).op ⋙ G.obj).RepresentableBy
    ((finiteEtaleToEtale (𝒰.X i)).obj (W i)))
lemma etaleLocalRepresenterGluingData_app (i : 𝒰.I₀) :
    (etaleLocalRepresenterGluingData G 𝒰 W h).natTrans.app i = (W i).hom
EtaleCohomology.etaleLocalRepresenterGluingData_isFiniteEtale

The actual glued morphism is finite étale, by its cartesian local models.

Source context 7 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open AlgebraicGeometry CategoryTheory Limits SchemeTheory.WeilRestriction
universe u v
namespace EtaleCohomology
variable {X : Scheme.{u}} (G : Sheaf X.smallEtaleTopology (Type u))
  (𝒰 : X.OpenCover) [Category.{v} 𝒰.I₀] [𝒰.LocallyDirected]
variable (W : ∀ i : 𝒰.I₀, FiniteEtale (𝒰.X i))
  (h : ∀ i : 𝒰.I₀, ((etalePostcompose (𝒰.f i)).op ⋙ G.obj).RepresentableBy
    ((finiteEtaleToEtale (𝒰.X i)).obj (W i)))
variable [Quiver.IsThin 𝒰.I₀] [Small.{u} 𝒰.I₀]
lemma etaleLocalRepresenterGluingData_isFiniteEtale :
    IsFiniteEtale (etaleLocalRepresenterGluingData G 𝒰 W h).toBase
EtaleCohomology.etaleGluedLocalRepresenter

The finite étale scheme obtained by gluing the given local representers.

Source context 7 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open AlgebraicGeometry CategoryTheory Limits SchemeTheory.WeilRestriction
universe u v
namespace EtaleCohomology
variable {X : Scheme.{u}} (G : Sheaf X.smallEtaleTopology (Type u))
  (𝒰 : X.OpenCover) [Category.{v} 𝒰.I₀] [𝒰.LocallyDirected]
variable (W : ∀ i : 𝒰.I₀, FiniteEtale (𝒰.X i))
  (h : ∀ i : 𝒰.I₀, ((etalePostcompose (𝒰.f i)).op ⋙ G.obj).RepresentableBy
    ((finiteEtaleToEtale (𝒰.X i)).obj (W i)))
variable [Quiver.IsThin 𝒰.I₀] [Small.{u} 𝒰.I₀]
def etaleGluedLocalRepresenter : FiniteEtale X
EtaleCohomology.etaleGluedLocalRepresenter_isPullback

Each original local representer is the genuine pullback of the glued scheme.

Source context 7 commands

Surrounding namespaces, section variables, and local commands at this declaration.

noncomputable section
open AlgebraicGeometry CategoryTheory Limits SchemeTheory.WeilRestriction
universe u v
namespace EtaleCohomology
variable {X : Scheme.{u}} (G : Sheaf X.smallEtaleTopology (Type u))
  (𝒰 : X.OpenCover) [Category.{v} 𝒰.I₀] [𝒰.LocallyDirected]
variable (W : ∀ i : 𝒰.I₀, FiniteEtale (𝒰.X i))
  (h : ∀ i : 𝒰.I₀, ((etalePostcompose (𝒰.f i)).op ⋙ G.obj).RepresentableBy
    ((finiteEtaleToEtale (𝒰.X i)).obj (W i)))
variable [Quiver.IsThin 𝒰.I₀] [Small.{u} 𝒰.I₀]
lemma etaleGluedLocalRepresenter_isPullback (i : 𝒰.I₀) :
    IsPullback (W i).hom
      (colimit.ι (etaleLocalRepresenterGluingData G 𝒰 W h).functor i)
      (𝒰.f i) (etaleGluedLocalRepresenter G 𝒰 W h).hom