Module

OpenGenericRootMembership.lean

Nyll.JacobianVarieties.Kummer.OpenGenericRootMembership
1 declaration indexed from sourceView source ↗

Actual finite étale Kummer roots are unramified away from the boundary

The condition defining the divisorial open Kummer group is proved from the actual cover, using the actual local rings of the open curve.

Declarations

AlgebraicCurve.CurveModel.mem_openKummerUnits_of_finiteEtale_generic_root
Source context 5 commands

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

noncomputable section
open CategoryTheory CategoryTheory.Limits AlgebraicGeometry
namespace AlgebraicCurve.CurveModel
attribute [local instance] CurveModel.isIntegral CurveModel.isProper CurveModel.smooth
variable {K F : Type} [Field K] [IsAlgClosed K] [Field F] [Algebra K F]
theorem mem_openKummerUnits_of_finiteEtale_generic_root
    (M : CurveModel K F) {X : Scheme} [IsIntegral X]
    (j : X ⟶ M.C) [IsOpenImmersion j]
    (L : Type) [Field L] [Algebra X.functionField L]
    {Y : Scheme} (f : Y ⟶ X) [IsFinite f] [Etale f]
    (e : pullback f (X.fromSpecStalk (genericPoint X)) ≅ Spec (.of L))
    (he : e.hom ≫ Spec.map (CommRingCat.ofHom (algebraMap X.functionField L)) =
      pullback.snd f (X.fromSpecStalk (genericPoint X)))
    (a : X.functionFieldˣ) (b : L) (n : ℕ+)
    (hb : b ^ (n : ℕ) = algebraMap X.functionField L (a : X.functionField)) :
    Units.map (M.ffEquiv.trans j.functionFieldRingEquivOfIsOpenImmersion).symm.toMonoidHom a ∈
      Pic0.openKummerUnits K F (M.openBoundaryPlaces j) n