Module

InverseLimitEquality.lean

Nyll.SchemeTheory.FiniteEtale.InverseLimitEquality
1 declaration indexed from sourceView source ↗

Eventual equality of native finite-etale morphisms

Equality after pullback to the actual inverse limit is detected by a genuine later stage. The maps in the conclusion are the native finite-etale pullback maps, so the result applies directly to inverse and cocycle equations.

Declarations

AlgebraicGeometry.FiniteEtale.exists_inverse_limit_stage_map_eq

Two morphisms of finite-etale covers whose native pullbacks to the limit agree have equal native pullbacks at a later original stage.

Source context 4 commands

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

noncomputable section
universe u
open CategoryTheory Limits
namespace AlgebraicGeometry.FiniteEtale
theorem exists_inverse_limit_stage_map_eq
    {I : Type u} [Category.{u} I] [IsCofiltered I]
    (D : I ⥤ Scheme.{u}) (c : Cone D) (hc : IsLimit c)
    [∀ {i j : I} (h : i ⟶ j), IsAffineHom (D.map h)]
    [∀ i : I, CompactSpace (D.obj i)]
    (i : I) {A B : FiniteEtale (D.obj i)} (a b : A ⟶ B)
    (hab : (FiniteEtale.pullback (c.π.app i)).map a =
      (FiniteEtale.pullback (c.π.app i)).map b) :
    ∃ (j : I) (hji : j ⟶ i),
      (FiniteEtale.pullback (D.map hji)).map a =
        (FiniteEtale.pullback (D.map hji)).map b