Module

LocalCyclotomicEmbedding.lean

Nyll.ClassFieldTheory.KroneckerWeber.LocalCyclotomicEmbedding
6 declarations indexed from sourceView source ↗

Local cyclotomic embeddings for the global construction

This module proves local Kronecker--Weber through norm-subgroup order reversal, then applies it to localizations of finite abelian extensions of ℚ.

Declarations

KroneckerWeber.exists_pPowerCyclotomicEmbedding_of_padicPrime_mem_normSubgroup

The ramified cyclotomic branch of local Kronecker–Weber. When the chosen prime element p is already a norm from L, the ramified realization theorem realizes the principal-unit depth furnished by openness as an actual p-power cyclotomic extension. Order reversal then embeds L into that extension.

The extra norm condition is exactly what excludes the nontrivial unramified part; the general construction also adjoins roots of unity of order p ^ f - 1.

Source context 5 commands

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

noncomputable section
namespace KroneckerWeber
open LocalFieldTheory RamificationTheory CyclicCohomology KummerTheory
open ClassFormation LocalClassFieldTheory
open LocalFieldTheory.Padic
theorem exists_pPowerCyclotomicEmbedding_of_padicPrime_mem_normSubgroup
    (p : ℕ) [Fact p.Prime]
    (L : Type) [Field L] [Algebra ℚ_[p] L]
    [FiniteDimensional ℚ_[p] L] [IsAbelianGalois ℚ_[p] L]
    (hpNorm : padicPrimeUnit p ∈ localNormSubgroup ℚ_[p] L) :
    ∃ n : ℕ, 1 ≤ n ∧
      ∃ ζ : CyclotomicField (p ^ n) ℚ_[p],
        IsPrimitiveRoot ζ (p ^ n) ∧
          Algebra.adjoin ℚ_[p] ({ζ} : Set _) = ⊤ ∧
          Nonempty (L →ₐ[ℚ_[p]] CyclotomicField (p ^ n) ℚ_[p])
KroneckerWeber.exists_structuredLocalCyclotomicEmbedding

Structured form of local Kronecker--Weber. The construction uses the cyclotomic order (p ^ f - 1) * p ^ n; retaining that form makes its unramified and p-primary ramified factors available to the global proof.

Openness supplies positive f,n with ⟨p ^ f⟩ Uⁿ ≤ N(Lˣ). The unramified cyclotomic theorem realizes ⟨p ^ f⟩ U¹ by the extension of order p ^ f - 1, while the ramified cyclotomic theorem realizes ⟨p⟩ Uⁿ by the p ^ n-cyclotomic extension. Their composite sits in the cyclotomic field of order (p ^ f - 1) * p ^ n, and the norm-subgroup order reversal gives the required embedding.

Source context 5 commands

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

noncomputable section
namespace KroneckerWeber
open LocalFieldTheory RamificationTheory CyclicCohomology KummerTheory
open ClassFormation LocalClassFieldTheory
open LocalFieldTheory.Padic
theorem exists_structuredLocalCyclotomicEmbedding
    (p : ℕ) [Fact p.Prime]
    (L : Type) [Field L] [Algebra ℚ_[p] L]
    [FiniteDimensional ℚ_[p] L] [IsAbelianGalois ℚ_[p] L] :
    ∃ f n : ℕ, 0 < f ∧ 1 ≤ n ∧
      ∃ ζ : CyclotomicField ((p ^ f - 1) * p ^ n) ℚ_[p],
        IsPrimitiveRoot ζ ((p ^ f - 1) * p ^ n) ∧
          Algebra.adjoin ℚ_[p] ({ζ} : Set _) = ⊤ ∧
          Nonempty
            (L →ₐ[ℚ_[p]]
              CyclotomicField ((p ^ f - 1) * p ^ n) ℚ_[p])
KroneckerWeber.exists_localCyclotomicEmbedding

Local Kronecker--Weber: every finite abelian extension of ℚ_p embeds in a cyclotomic extension.

Source context 5 commands

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

noncomputable section
namespace KroneckerWeber
open LocalFieldTheory RamificationTheory CyclicCohomology KummerTheory
open ClassFormation LocalClassFieldTheory
open LocalFieldTheory.Padic
theorem exists_localCyclotomicEmbedding
    (p : ℕ) [Fact p.Prime]
    (L : Type) [Field L] [Algebra ℚ_[p] L]
    [FiniteDimensional ℚ_[p] L] [IsAbelianGalois ℚ_[p] L] :
    ∃ m : ℕ, 0 < m ∧
      ∃ ζ : CyclotomicField m ℚ_[p],
        IsPrimitiveRoot ζ m ∧
          Algebra.adjoin ℚ_[p] ({ζ} : Set _) = ⊤ ∧
          Nonempty (L →ₐ[ℚ_[p]] CyclotomicField m ℚ_[p])
KroneckerWeber.globalPadicLocalizationCyclotomicAlgHom

The type of actual embeddings of the localization at w into the m-th cyclotomic extension of ℚ_p. Naming this type exposes an embedding as a genuine theorem input while keeping all transported algebra instances internal.

Source context 6 commands

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

noncomputable section
namespace KroneckerWeber
open AlgebraicNumberTheory.Valuations
open HilbertRamification
variable (p : ℕ) [Fact p.Prime]
variable (L : Type) [Field L] [Algebra ℚ L]
  [FiniteDimensional ℚ L] [IsAbelianGalois ℚ L]
def globalPadicLocalizationCyclotomicAlgHom
    (w : AbsoluteValueExtension (Rat.AbsoluteValue.padic p) L)
    (m : ℕ) : Type
KroneckerWeber.globalPadicLocalizationStructuredCyclotomicEmbeddingProperty

Structured version of the local cyclotomic-embedding assertion. It retains the prime-to-p unramified order p ^ f - 1 and the ramified order p ^ n from the local cyclotomic construction.

Source context 6 commands

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

noncomputable section
namespace KroneckerWeber
open AlgebraicNumberTheory.Valuations
open HilbertRamification
variable (p : ℕ) [Fact p.Prime]
variable (L : Type) [Field L] [Algebra ℚ L]
  [FiniteDimensional ℚ L] [IsAbelianGalois ℚ L]
def globalPadicLocalizationStructuredCyclotomicEmbeddingProperty
    (w : AbsoluteValueExtension (Rat.AbsoluteValue.padic p) L) : Prop
KroneckerWeber.globalPadicLocalization_structuredCyclotomicEmbedding

The local completion of a finite abelian extension of ℚ, transported to the concrete base ℚ_[p], embeds in a cyclotomic extension.

This is the local cyclotomic input to the global construction. It does not yet assert that the local embeddings for the finitely many ramified primes glue into one global cyclotomic field.

Source context 6 commands

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

noncomputable section
namespace KroneckerWeber
open AlgebraicNumberTheory.Valuations
open HilbertRamification
variable (p : ℕ) [Fact p.Prime]
variable (L : Type) [Field L] [Algebra ℚ L]
  [FiniteDimensional ℚ L] [IsAbelianGalois ℚ L]
theorem globalPadicLocalization_structuredCyclotomicEmbedding
    (w : AbsoluteValueExtension (Rat.AbsoluteValue.padic p) L) :
    globalPadicLocalizationStructuredCyclotomicEmbeddingProperty p L w