Module

MovingRootOfUnity.lean

Nyll.GaloisCohomology.Kummer.Concrete.MovingRootOfUnity
1 declaration indexed from sourceView source ↗

Moving a root of unity outside the base field

If not all roots of a given order lie in the base field of a finite Galois extension, a primitive root is moved by an actual Galois automorphism.

Imports3
  • Mathlib.Data.PNat.Defs
  • Mathlib.FieldTheory.Galois.Basic
  • Mathlib.RingTheory.RootsOfUnity.PrimitiveRoots
Imported by2

Declarations

KummerTheory.exists_moving_primitiveRoot_of_not_all_roots_in_base

A primitive root is moved by a Galois automorphism when the roots at its level do not all come from the base field.

Source context 2 commands

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

namespace KummerTheory
variable (L E : Type*) [Field L] [Field E] [Algebra L E]
  [FiniteDimensional L E] [IsGalois L E]
theorem exists_moving_primitiveRoot_of_not_all_roots_in_base
    (m : ℕ+) (hmu : (primitiveRoots (m : ℕ) E).Nonempty)
    (hnot : ¬ ∀ ξ : E, ξ ^ (m : ℕ) = 1 →
      ξ ∈ Set.range (algebraMap L E)) :
    ∃ (ζ : E) (τ : Gal(E/L)), IsPrimitiveRoot ζ (m : ℕ) ∧ τ ζ ≠ ζ