Module

ResidueMapCoefficientNaturality.lean

Nyll.EtaleFundamentalGroups.Inertia.ResidueMapCoefficientNaturality
1 declaration indexed from sourceView source ↗

Descending a literal coefficient square to residue fields

This ring-only lemma uses coefficient surjectivity at a maximal ideal. Its applications supply the two coefficient formulas and square from actual maps.

Declarations

EtaleFundamentalGroups.Inertia.residueMap_coefficient_naturality
Source context 2 commands

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

namespace EtaleFundamentalGroups.Inertia
universe u v
theorem residueMap_coefficient_naturality
    {B : Type u} {C : Type v} [CommRing B] [CommRing C]
    (P : Ideal B) [P.IsMaximal] (Q : Ideal C) [Q.IsPrime]
    (j : B →+* C) (hj : P = Q.comap j)
    (s : B →+* B) (t : C →+* C)
    (a : P.ResidueField →+* P.ResidueField)
    (b : Q.ResidueField →+* Q.ResidueField)
    (ha : ∀ x : B, a.toFun ((algebraMap B P.ResidueField).toFun x) =
      (algebraMap B P.ResidueField).toFun (s.toFun x))
    (hb : ∀ x : C, b.toFun ((algebraMap C Q.ResidueField).toFun x) =
      (algebraMap C Q.ResidueField).toFun (t.toFun x))
    (hcomm : j.comp s = t.comp j) (x : P.ResidueField) :
    (Ideal.ResidueField.map P Q j hj).toFun (a.toFun x) =
      b.toFun ((Ideal.ResidueField.map P Q j hj).toFun x)