Module

PrimeQuotientCoefficients.lean

Nyll.EtaleFundamentalGroups.Purity.PrimeQuotientCoefficients
2 declarations indexed from sourceView source ↗

Scalars on modules isomorphic to prime quotients

The residue field is annihilated by the maximal ideal. For any other prime quotient of a local ring, an element of the maximal ideal outside the prime acts regularly. These properties transfer along a coefficient linear equivalence without constructing a map on local cohomology.

Imports4
  • Mathlib.RingTheory.Ideal.Quotient.Basic
  • Mathlib.RingTheory.LocalRing.MaximalIdeal.Basic
  • Mathlib.RingTheory.Regular.IsSMulRegular
  • Mathlib.RingTheory.Spectrum.Prime.Basic
Imported by2

Declarations

EtaleFundamentalGroups.Purity.maximalIdeal_smul_eq_zero_of_equiv_residueField

The maximal ideal kills any module linearly equivalent to the residue field.

Source context 5 commands

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

namespace EtaleFundamentalGroups.Purity
universe u v
open IsLocalRing
variable {R : Type u} [CommRing R] [IsLocalRing R]
variable {N : Type v} [AddCommGroup N] [Module R N]
theorem maximalIdeal_smul_eq_zero_of_equiv_residueField
    (e : N ≃ₗ[R] (R ⧸ maximalIdeal R))
    (a : R) (ha : a ∈ maximalIdeal R) (z : N) : a • z = 0
EtaleFundamentalGroups.Purity.exists_regular_maximalIdeal_scalar_of_equiv_primeQuotient

A prime quotient different from the residue field admits a regular scalar in the maximal ideal, also after transporting the coefficients along a linear equivalence.

Source context 5 commands

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

namespace EtaleFundamentalGroups.Purity
universe u v
open IsLocalRing
variable {R : Type u} [CommRing R] [IsLocalRing R]
variable {N : Type v} [AddCommGroup N] [Module R N]
theorem exists_regular_maximalIdeal_scalar_of_equiv_primeQuotient
    (p : PrimeSpectrum R) (e : N ≃ₗ[R] (R ⧸ p.asIdeal))
    (hp : p.asIdeal ≠ maximalIdeal R) :
    ∃ x : R, x ∈ maximalIdeal R ∧ IsSMulRegular N x