Module

ContinuousCharacters.lean

Nyll.GaloisCohomology.Kummer.Concrete.ContinuousCharacters
3 declarations indexed from sourceView source ↗

Finite-stage factorization of continuous Galois characters

A continuous character from an infinite Galois group to a discrete group factors through the Galois group of a finite Galois intermediate field.

Imports3
  • Mathlib.FieldTheory.Galois.Infinite
  • Mathlib.FieldTheory.Galois.Profinite
  • Mathlib.Topology.Algebra.ContinuousMonoidHom
Imported by2

Declarations

KummerTheory.continuousCharacterIsOpenKer
Source context 4 commands

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

noncomputable section
namespace KummerTheory
open scoped Topology
variable {K Ω A : Type*}
  [Field K] [Field Ω] [Algebra K Ω]
  [Group A] [TopologicalSpace A] [DiscreteTopology A]
theorem continuousCharacterIsOpenKer (χ : Gal(Ω/K) →ₜ* A) :
    IsOpen (χ.toMonoidHom.ker : Set Gal(Ω/K))
KummerTheory.continuousCharacterExistsFiniteGaloisFixingSubgroupLeKer
Source context 5 commands

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

noncomputable section
namespace KummerTheory
open scoped Topology
variable {K Ω A : Type*}
  [Field K] [Field Ω] [Algebra K Ω]
  [Group A] [TopologicalSpace A] [DiscreteTopology A]
variable [IsGalois K Ω]
theorem continuousCharacterExistsFiniteGaloisFixingSubgroupLeKer
    (χ : Gal(Ω/K) →ₜ* A) :
    ∃ E : FiniteGaloisIntermediateField K Ω,
      E.fixingSubgroup ≤ χ.toMonoidHom.ker
KummerTheory.continuousCharacter_factors_through_finiteGalois

Every continuous character of an infinite Galois group into a discrete group factors through the Galois group of a finite Galois intermediate field.

Source context 5 commands

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

noncomputable section
namespace KummerTheory
open scoped Topology
variable {K Ω A : Type*}
  [Field K] [Field Ω] [Algebra K Ω]
  [Group A] [TopologicalSpace A] [DiscreteTopology A]
variable [IsGalois K Ω]
theorem continuousCharacter_factors_through_finiteGalois
    (χ : Gal(Ω/K) →ₜ* A) :
    ∃ (E : FiniteGaloisIntermediateField K Ω) (χE : Gal(E/K) →* A),
      χE.comp (AlgEquiv.restrictNormalHom E) = χ.toMonoidHom