Pro-étale cohomology

2.5. Bijective on stalks and ind-Zariski🔗

Lemma2.5.1
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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Let A \to B be a w-local ring map of w-local rings that identifies local rings. Then A \to B is ind-Zariski. (Stacks Project, Tag 097F)

Lean code for Lemma2.5.11 theorem, incomplete
  • theoremdefined in Proetale/Algebra/IndBijectiveOnStalks.lean
    contains sorry
    theorem RingHom.BijectiveOnStalks.indZariski_of_isWLocal.{u} {R S : Type u}
      [CommRing R] [CommRing S] {f : R →+* S} [IsWLocalRing R]
      [IsWLocalRing S] (hf : f.IsWLocal) (hf' : f.BijectiveOnStalks) :
      f.IndZariski
    theorem RingHom.BijectiveOnStalks.indZariski_of_isWLocal.{u}
      {R S : Type u} [CommRing R] [CommRing S]
      {f : R →+* S} [IsWLocalRing R]
      [IsWLocalRing S] (hf : f.IsWLocal)
      (hf' : f.BijectiveOnStalks) :
      f.IndZariski
    A w-local ring map between w-local spaces that is bijective on stalks is ind-Zariski. 
Proposition2.5.2
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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Let A \to B be a ring map that is bijective on stalks. Then there exists a faithfully flat, ind-Zariski map B \to B' such that A \to B' is ind-Zariski. (Stacks Project, Tag 097G)

Lean code for Proposition2.5.22 theorems, 1 incomplete
  • theoremdefined in Proetale/Algebra/IndBijectiveOnStalks.lean
    contains sorry
    theorem Algebra.BijectiveOnStalks.exists_indZariski.{u} (R S : Type u)
      [CommRing R] [CommRing S] [Algebra R S]
      [Algebra.BijectiveOnStalks R S] :
       T x x_1 x_2,
         (_ : IsScalarTower R S T),
          Algebra.IndZariski S T 
            Module.FaithfullyFlat S T  Algebra.IndZariski R T
    theorem Algebra.BijectiveOnStalks.exists_indZariski.{u}
      (R S : Type u) [CommRing R] [CommRing S]
      [Algebra R S]
      [Algebra.BijectiveOnStalks R S] :
       T x x_1 x_2,
         (_ : IsScalarTower R S T),
          Algebra.IndZariski S T 
            Module.FaithfullyFlat S T 
              Algebra.IndZariski R T
  • theoremdefined in Proetale/Algebra/IndBijectiveOnStalks.lean
    complete
    theorem RingHom.BijectiveOnStalks.exists_indZariski.{u} {R S : Type u}
      [CommRing R] [CommRing S] {f : R →+* S} (hf : f.BijectiveOnStalks) :
       T x g, g.IndZariski  g.FaithfullyFlat  (g.comp f).IndZariski
    theorem RingHom.BijectiveOnStalks.exists_indZariski.{u}
      {R S : Type u} [CommRing R] [CommRing S]
      {f : R →+* S}
      (hf : f.BijectiveOnStalks) :
       T x g,
        g.IndZariski 
          g.FaithfullyFlat 
            (g.comp f).IndZariski
    If `R → S` is bijective on stalks, ind-Zariski locally it is ind-Zariski. 
Proof for Proposition 2.5.2
Proof uses 3
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Lemma 1.1.32
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By Lemma 1.1.32, the induced map A_w \to B_w is again bijective on stalks and hence ind-Zariski by Lemma 2.5.1. Since B \to B_w is ind-Zariski and faithfully flat and the composition A \to B \to B_w is ind-Zariski, the claim follows.