Module

Stalks.lean

Nyll.EtaleCohomology.Sites.Stalks
5 declarations indexed from sourceView source ↗

Geometric stalks and exactness on the small étale site

At a point of a scheme, use the separable closure of its residue field to obtain a geometric point and its filtered-colimit stalk functor. The existing conservativity of this family of geometric points detects the vanishing of homology, hence exactness of sequences of coefficient sheaves.

Imports10
  • Mathlib.Algebra.Category.ModuleCat.AB
  • Mathlib.Algebra.Category.ModuleCat.Adjunctions
  • Mathlib.Algebra.Category.ModuleCat.FilteredColimits
  • Mathlib.AlgebraicGeometry.Sites.AffineEtale
  • Mathlib.AlgebraicGeometry.Sites.EtalePoint
  • Mathlib.CategoryTheory.Sites.Point.Basic
  • Mathlib.CategoryTheory.Sites.Point.Conservative
  • Mathlib.CategoryTheory.Sites.Point.Skyscraper
  • Mathlib.Algebra.Homology.ShortComplex.Exact
  • Mathlib.Algebra.Homology.ShortComplex.ShortExact
Imported by5

Declarations

EtaleCohomology.residueStalk

The geometric stalk at the separable closure of the residue field of a point.

Source context 5 commands

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

noncomputable section
universe u
open AlgebraicGeometry CategoryTheory CategoryTheory.Limits
namespace EtaleCohomology
variable (X : Scheme.{u}) (R : Type u) [CommRing R]
def residueStalk (x : X) : Sheaf X.smallEtaleTopology (ModuleCat.{u} R) ⥤ ModuleCat.{u} R
Source context 5 commands

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

noncomputable section
universe u
open AlgebraicGeometry CategoryTheory CategoryTheory.Limits
namespace EtaleCohomology
variable (X : Scheme.{u}) (R : Type u) [CommRing R]
instance (x : X) : PreservesFiniteLimits (residueStalk X R x)
Source context 5 commands

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

noncomputable section
universe u
open AlgebraicGeometry CategoryTheory CategoryTheory.Limits
namespace EtaleCohomology
variable (X : Scheme.{u}) (R : Type u) [CommRing R]
instance (x : X) : PreservesFiniteColimits (residueStalk X R x)
EtaleCohomology.exact_iff_residueStalk

Exactness of coefficient sheaves is detected on these geometric stalks.

Source context 5 commands

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

noncomputable section
universe u
open AlgebraicGeometry CategoryTheory CategoryTheory.Limits
namespace EtaleCohomology
variable (X : Scheme.{u}) (R : Type u) [CommRing R]
lemma exact_iff_residueStalk (S : ShortComplex (Sheaf X.smallEtaleTopology (ModuleCat.{u} R))) :
    S.Exact ↔ ∀ x : X, (S.map (residueStalk X R x)).Exact
EtaleCohomology.shortExact_iff_residueStalk

Short exactness is likewise equivalent to short exactness at every geometric stalk.

Source context 5 commands

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

noncomputable section
universe u
open AlgebraicGeometry CategoryTheory CategoryTheory.Limits
namespace EtaleCohomology
variable (X : Scheme.{u}) (R : Type u) [CommRing R]
lemma shortExact_iff_residueStalk
    (S : ShortComplex (Sheaf X.smallEtaleTopology (ModuleCat.{u} R))) :
    S.ShortExact ↔ ∀ x : X, (S.map (residueStalk X R x)).ShortExact