Module

CompletionFormalComparison.lean

Nyll.EtaleFundamentalGroups.Purity.CompletionFormalComparison
1 declaration indexed from sourceView source ↗

Formally étale maps into adically complete rings

Formal smoothness lifts a map from the first infinitesimal quotient to an adically complete target. Adic separatedness and formal unramifiedness make that lift unique. Thus reduction modulo the ideal is bijective on maps from a formally étale algebra.

Imports2
  • Mathlib.RingTheory.Etale.Basic
  • Mathlib.RingTheory.Smooth.AdicCompletion
Imported by2

Declarations

Algebra.FormallyEtale.comp_bijective_of_isAdicComplete

Maps from a formally étale algebra to an adically complete algebra are uniquely determined by, and uniquely lift from, their reduction modulo the ideal of definition.

Source context 5 commands

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

namespace Algebra.FormallyEtale
universe u v w
variable {R : Type u} {A : Type v} {S : Type w}
variable [CommRing R] [CommRing A] [CommRing S]
variable [Algebra R A] [Algebra R S]
theorem comp_bijective_of_isAdicComplete [FormallyEtale R A]
    (I : Ideal S) [IsAdicComplete I S] :
    Function.Bijective
      ((Ideal.Quotient.mkₐ R I).comp :
        (A →ₐ[R] S) → A →ₐ[R] S ⧸ I)