Module

FiniteAbelianLocalReciprocityUnramifiedHomExt.lean

Nyll.ClassFieldTheory.Theorems.LocalClassFieldTheory.FiniteAbelianLocalReciprocityUnramifiedHomExt
1 declaration indexed from sourceView source ↗

Uniqueness from an unramified norm kernel and a uniformizer value

For a fixed finite unramified abelian extension, the norm subgroup contains every integer unit. The decomposition of a field unit into an integer unit and a power of an inverse uniformizer therefore determines a homomorphism with this kernel from its value on that inverse uniformizer.

This is the unramified generator step, not uniqueness of finite local Artin maps for ramified extensions.

Declarations

ClassFieldTheory.finiteAbelianLocalReciprocity_unramified_hom_ext

For an unramified extension, two norm-kernel homomorphisms that agree on one inverse uniformizer agree on all field units.

Source context 4 commands

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

open scoped ValuativeRel
open LocalFieldTheory.IsNonarchimedeanLocalField
noncomputable section
namespace ClassFieldTheory
theorem finiteAbelianLocalReciprocity_unramified_hom_ext
    (K L : Type)
    [Field K] [ValuativeRel K] [TopologicalSpace K]
    [IsNonarchimedeanLocalField K]
    [Field L] [ValuativeRel L] [TopologicalSpace L]
    [IsNonarchimedeanLocalField L]
    [Algebra K L] [FiniteDimensional K L] [IsAbelianGalois K L]
    [Valuation.HasExtension (ValuativeRel.valuation K)
      (ValuativeRel.valuation L)]
    (hUnram : (𝓂[L] : Ideal 𝒪[L]).ramificationIdx 𝒪[K] = 1)
    (π : 𝒪[K])
    (hπ : (ValuativeRel.valuation K).IsUniformizer (π : K))
    (f g : Kˣ →ₜ* (L ≃ₐ[K] L))
    (hfker : f.toMonoidHom.ker = fieldNormSubgroup K L)
    (hgker : g.toMonoidHom.ker = fieldNormSubgroup K L)
    (hϖ : f ((Units.mk0 (π : K) hπ.ne_zero)⁻¹) =
      g ((Units.mk0 (π : K) hπ.ne_zero)⁻¹)) :
    f = g