Module

ZariskiSectionEquality.lean

Nyll.EtaleCohomology.Sites.ZariskiSectionEquality
1 declaration indexed from sourceView source ↗

Equality of étale sections on an actual Zariski neighborhood

An étale neighborhood covers its open image. The small-site sheaf separation axiom therefore turns equality on that neighborhood into equality on its actual open image in the original scheme.

Imports6
  • Nyll.EtaleCohomology.Sites.ZariskiRestriction
  • Mathlib.AlgebraicGeometry.Sites.Etale
  • Mathlib.AlgebraicGeometry.Restrict
  • Mathlib.CategoryTheory.Sites.LocallyInjective
  • Mathlib.CategoryTheory.Sites.Whiskering
  • Mathlib.CategoryTheory.Types.Basic
Imported by2

Declarations

EtaleCohomology.exists_zariski_neighborhood_sections_eq_of_etale_map_eq

Equality after restriction to an étale neighborhood gives equality on an actual open neighborhood of each point in its image.

Source context 4 commands

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

noncomputable section
universe u
open AlgebraicGeometry CategoryTheory TopologicalSpace Opposite
namespace EtaleCohomology
theorem exists_zariski_neighborhood_sections_eq_of_etale_map_eq
    {X : Scheme.{u}} (F : Sheaf X.smallEtaleTopology (Type u))
    (U : X.Opens) (a b : F.obj.obj (op ((zariskiToEtale X).obj U)))
    (V : X.Etale) (g : V ⟶ (zariskiToEtale X).obj U)
    (hab : F.obj.map g.op a = F.obj.map g.op b) (v : V.left) :
    ∃ (W : X.Opens) (hWU : W ≤ U), V.hom v ∈ W ∧
      F.obj.map ((zariskiToEtale X).map (homOfLE hWU)).op a =
        F.obj.map ((zariskiToEtale X).map (homOfLE hWU)).op b