Pro-étale cohomology

2.6. Weakly étale and ind-étale🔗

Theorem2.6.1
Group: Weakly étale ring maps, weak dimension, and the comparison between weakly étale and ind-étale, following Section 2 of Bhatt–Scholze and the Stacks Project. (45)
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Lemma 2.1
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uses 0used by 1L∃∀N

Let R \to S be weakly étale. Then there exists a faithfully flat ind-étale morphism S \to T such that the composition R \to T is ind-étale.

Lean code for Theorem2.6.12 theorems, 1 incomplete
  • theoremdefined in Proetale/Algebra/IndWeaklyEtale.lean
    complete
    theorem RingHom.WeaklyEtale.exists_indEtale_comp.{u} {R S : Type u} [CommRing R]
      [CommRing S] {f : R →+* S} (hf : f.WeaklyEtale) :
       T x g, g.IndEtale  g.FaithfullyFlat  (g.comp f).IndEtale
    theorem RingHom.WeaklyEtale.exists_indEtale_comp.{u}
      {R S : Type u} [CommRing R] [CommRing S]
      {f : R →+* S} (hf : f.WeaklyEtale) :
       T x g,
        g.IndEtale 
          g.FaithfullyFlat 
            (g.comp f).IndEtale
    If `S` is a weakly étale `R`-algebra, there exists a faithfully flat, ind-étale `S`-algebra `T`
    such that `T` is an ind-étale `R`-algebra. 
  • theoremdefined in Proetale/Algebra/IndWeaklyEtale.lean
    contains sorry
    theorem Algebra.WeaklyEtale.exists_indEtale.{u} (R S : Type u) [CommRing R]
      [CommRing S] [Algebra R S] [Algebra.WeaklyEtale R S] :
       T x x_1 x_2,
         (_ : IsScalarTower R S T),
          Algebra.IndEtale S T 
            Module.FaithfullyFlat S T  Algebra.IndEtale R T
    theorem Algebra.WeaklyEtale.exists_indEtale.{u}
      (R S : Type u) [CommRing R] [CommRing S]
      [Algebra R S]
      [Algebra.WeaklyEtale R S] :
       T x x_1 x_2,
         (_ : IsScalarTower R S T),
          Algebra.IndEtale S T 
            Module.FaithfullyFlat S T 
              Algebra.IndEtale R T
    If `S` is a weakly étale `R`-algebra, there exists a faithfully flat, ind-étale `S`-algebra `T`
    such that `T` is an ind-étale `R`-algebra. 
Proof for Theorem 2.6.1
Proof uses 2
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Theorem 2.4.13
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TBA.