Pro-étale cohomology

1.1. Preliminaries🔗

Definition1.1.1
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Theorem 1.1.2
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A topological space X is extremally disconnected if the closure of every open subset is open.

Lean code for Definition1.1.11 definition
  • class(1 method)defined in Mathlib/Topology/ExtremallyDisconnected.lean
    complete
    class ExtremallyDisconnected.{u} (X : Type u) [TopologicalSpace X] : Prop
    class ExtremallyDisconnected.{u} (X : Type u)
      [TopologicalSpace X] : Prop
    An extremally disconnected topological space is a space
    in which the closure of every open set is open. 

    Methods

    open_closure :  (U : Set X), IsOpen U  IsOpen (closure U)
    The closure of every open set is open. 

The reason that we are interested in extremally disconnected spaces is the following theorem.

Theorem1.1.2
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a quasi-compact Hausdorff topological space. Then X is extremally disconnected if and only if it is a projective object in the category of quasi-compact Hausdorff spaces, i.e., for every continuous surjection f : Y \to Z of quasi-compact Hausdorff spaces and every continuous map g : X \to Z, there exists a continuous map h : X \to Y such that f \circ h = g.

Lean code for Theorem1.1.22 declarations
  • defdefined in Mathlib/Topology/Category/Stonean/Basic.lean
    complete
    def CompHaus.toStonean.{u} (X : CompHaus) [CategoryTheory.Projective X] :
      Stonean
    def CompHaus.toStonean.{u} (X : CompHaus)
      [CategoryTheory.Projective X] : Stonean
    `Projective` implies `Stonean`. 
  • theoremdefined in Mathlib/Topology/Category/Stonean/Basic.lean
    complete
    theorem Stonean.instProjectiveCompHausCompHaus.{u_1} (X : Stonean) :
      CategoryTheory.Projective (Stonean.toCompHaus.obj X)
    theorem Stonean.instProjectiveCompHausCompHaus.{u_1}
      (X : Stonean) :
      CategoryTheory.Projective
        (Stonean.toCompHaus.obj X)
    Every Stonean space is projective in `CompHaus` 
Definition1.1.3
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Theorem 1.1.4
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Let X be a topological space. The Stone-Čech compactification of X is the profinite space \beta(X) such that

  1. X is dense in \beta(X);

  2. every continuous map f \colon X \to Y to a quasi-compact Hausdorff space Y extends uniquely to a continuous map \beta(f) \colon \beta(X) \to Y.

We denote the Stone-Čech compactification of X by \beta(X).

Lean code for Definition1.1.31 definition
  • defdefined in Mathlib/Topology/Compactification/StoneCech.lean
    complete
    def StoneCech.{u} (α : Type u) [TopologicalSpace α] : Type u
    def StoneCech.{u} (α : Type u)
      [TopologicalSpace α] : Type u
    The Stone-Čech compactification of a topological space. 
Theorem1.1.4
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Definition 1.1.1
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Let X be a topological space. Then the Stone-Čech compactification \beta(X) is extremally disconnected.

Lean code for Theorem1.1.41 theorem
  • theoremdefined in Mathlib/Topology/ExtremallyDisconnected.lean
    complete
    theorem StoneCech.projective.{u} {X : Type u} [TopologicalSpace X]
      [DiscreteTopology X] : CompactT2.Projective (StoneCech X)
    theorem StoneCech.projective.{u} {X : Type u}
      [TopologicalSpace X]
      [DiscreteTopology X] :
      CompactT2.Projective (StoneCech X)
Proposition1.1.5
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Definition 1.1.1
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Let X be a quasi-compact Hausdorff space. There exists a continuous surjection X' \to X with X' quasi-compact, Hausdorff, and extremally disconnected. (Stacks Project, Tag 090D)

Lean code for Proposition1.1.54 declarations
  • defdefined in Mathlib/Topology/Category/Stonean/Basic.lean
    complete
    def CompHaus.presentation.{u_1} (X : CompHaus) : Stonean
    def CompHaus.presentation.{u_1}
      (X : CompHaus) : Stonean
    If `X` is compact Hausdorff, `presentation X` is a Stonean space equipped with an epimorphism
    down to `X` (see `CompHaus.presentation.π` and `CompHaus.presentation.epi_π`). It is a
    "constructive" witness to the fact that `CompHaus` has enough projectives. 
  • defdefined in Mathlib/Topology/Category/Stonean/Basic.lean
    complete
    def CompHaus.presentation.π.{u_1} (X : CompHaus) :
      Stonean.toCompHaus.obj X.presentation  X
    def CompHaus.presentation.π.{u_1}
      (X : CompHaus) :
      Stonean.toCompHaus.obj X.presentation 
        X
    The morphism from `presentation X` to `X`. 
  • theoremdefined in Mathlib/Topology/Category/Stonean/Basic.lean
    complete
    theorem CompHaus.presentation.epi_π.{u_1} (X : CompHaus) :
      CategoryTheory.Epi (CompHaus.presentation.π X)
    theorem CompHaus.presentation.epi_π.{u_1}
      (X : CompHaus) :
      CategoryTheory.Epi
        (CompHaus.presentation.π X)
    The morphism from `presentation X` to `X` is an epimorphism. 
  • defdefined in Mathlib/Topology/Category/Stonean/Basic.lean
    complete
    def CompHaus.lift.{u_1} {X Y : CompHaus} {Z : Stonean} (e : Z.compHaus  Y)
      (f : X  Y) [CategoryTheory.Epi f] : Z.compHaus  X
    def CompHaus.lift.{u_1} {X Y : CompHaus}
      {Z : Stonean} (e : Z.compHaus  Y)
      (f : X  Y) [CategoryTheory.Epi f] :
      Z.compHaus  X
    ```
                   X
                   |
                  (f)
                   |
                   \/
      Z ---(e)---> Y
    ```
    If `Z` is a Stonean space, `f : X ⟶ Y` an epi in `CompHaus` and `e : Z ⟶ Y` is arbitrary, then
    `lift e f` is a fixed (but arbitrary) lift of `e` to a morphism `Z ⟶ X`. It exists because
    `Z` is a projective object in `CompHaus`.
    
Proof for Proposition 1.1.5

Let Y = X but endowed with the discrete topology. Let X' = \beta(Y), which is extremally disconnected by Theorem 1.1.4. The continuous map Y \to X factors as Y \to X' \to X.

We need the following lemmas about connected components. (Note by Jiedong: This is WRONG. In general, \pi_0(X) \times \pi_0(Y) is continuous and bijective, but not necessarily homeomorphic.)

Lemma1.1.6
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X, Y be topological spaces. Then we have \pi_0 (X \times Y) \simeq \pi_0(X) \times \pi_0(Y) as topological spaces.

Lean code for Lemma1.1.64 declarations, 1 incomplete
  • theoremdefined in Proetale/Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    theorem connectedComponent.prod.{u_2, u_3} (S : Type u_2) (T : Type u_3)
      [TopologicalSpace S] [TopologicalSpace T] (s : S) (t : T) :
      connectedComponent (s, t) =
        connectedComponent s ×ˢ connectedComponent t
    theorem connectedComponent.prod.{u_2, u_3}
      (S : Type u_2) (T : Type u_3)
      [TopologicalSpace S]
      [TopologicalSpace T] (s : S) (t : T) :
      connectedComponent (s, t) =
        connectedComponent s ×ˢ
          connectedComponent t
  • theoremdefined in Proetale/Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    theorem ConnectedComponents.bijective_connectedComponentsLift_prod.{u_2, u_3}
      (S : Type u_2) (T : Type u_3) [TopologicalSpace S]
      [TopologicalSpace T] : Function.Bijective .connectedComponentsLift
    theorem ConnectedComponents.bijective_connectedComponentsLift_prod.{u_2,
        u_3}
      (S : Type u_2) (T : Type u_3)
      [TopologicalSpace S]
      [TopologicalSpace T] :
      Function.Bijective
        .connectedComponentsLift
  • theoremdefined in Proetale/Mathlib/Topology/Connected/TotallyDisconnected.lean
    contains sorry
    theorem ConnectedComponents.isHomeomorph_connectedComponentsLift_prod.{u_2, u_3}
      (S : Type u_2) (T : Type u_3) [TopologicalSpace S]
      [TopologicalSpace T] : IsHomeomorph .connectedComponentsLift
    theorem ConnectedComponents.isHomeomorph_connectedComponentsLift_prod.{u_2,
        u_3}
      (S : Type u_2) (T : Type u_3)
      [TopologicalSpace S]
      [TopologicalSpace T] :
      IsHomeomorph .connectedComponentsLift
  • defdefined in Proetale/Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    def ConnectedComponents.prodMap.{u_2, u_3} {S : Type u_2} {T : Type u_3}
      [TopologicalSpace S] [TopologicalSpace T] :
      ConnectedComponents (S × T) ≃ₜ
        ConnectedComponents S × ConnectedComponents T
    def ConnectedComponents.prodMap.{u_2, u_3}
      {S : Type u_2} {T : Type u_3}
      [TopologicalSpace S]
      [TopologicalSpace T] :
      ConnectedComponents (S × T) ≃ₜ
        ConnectedComponents S ×
          ConnectedComponents T
Proof for Lemma 1.1.6
uses 0

Let x, y be points of X, Y, respectively. To show the above map is bijective, it suffices to show that the connected component of (x,y) in X \times Y is the product of the connected component of x in X and the connected component of y in Y. We know that the product of connected subsets is still connected (IsPreconnected.prod). The connected component of (x, y) cannot be larger because its projections to X and Y are also connected.

To show that the bijective map is homeomorphic, we notice that the topology on both sides is generated by the basis of the form \text{image } U \times \text{image } V.

Lemma1.1.7
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a totally disconnected topological space. Then X \simeq \pi_0(X) as topological spaces.

Lean code for Lemma1.1.71 definition
  • defdefined in Proetale/Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    def ConnectedComponents.mkHomeomorph.{u_2} (S : Type u_2)
      [TopologicalSpace S] [TotallyDisconnectedSpace S] :
      S ≃ₜ ConnectedComponents S
    def ConnectedComponents.mkHomeomorph.{u_2}
      (S : Type u_2) [TopologicalSpace S]
      [TotallyDisconnectedSpace S] :
      S ≃ₜ ConnectedComponents S
Proof for Lemma 1.1.7
uses 0

Use the universal property of connected components.

Lemma1.1.8
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X = \lim_i X_i be a limit of topological spaces over some index category I and let s \subseteq X be a subset of X. Denote by s_i the image of s in X_i. Then \overline{s} = \bigcap_i \pi_i^{-1} (\overline{s_i}), where \pi_i : X \to X_i is the projection map.

Lean code for Lemma1.1.81 theorem
  • theoremdefined in Proetale/Topology/Preliminaries/Closure.lean
    complete
    theorem TopCat.closure_eq_iInter_preimage_closure_image.{u, v, w} {I : Type v}
      [CategoryTheory.Category.{w, v} I] [CategoryTheory.IsCofiltered I]
      {F : CategoryTheory.Functor I TopCat}
      {C : CategoryTheory.Limits.Cone F}
      (hC : CategoryTheory.Limits.IsLimit C) (s : Set C.pt) :
      closure s =
         i,
          (CategoryTheory.ConcreteCategory.hom (C.π.app i)) ⁻¹'
            closure
              ((CategoryTheory.ConcreteCategory.hom (C.π.app i)) '' s)
    theorem TopCat.closure_eq_iInter_preimage_closure_image.{u,
        v, w}
      {I : Type v}
      [CategoryTheory.Category.{w, v} I]
      [CategoryTheory.IsCofiltered I]
      {F : CategoryTheory.Functor I TopCat}
      {C : CategoryTheory.Limits.Cone F}
      (hC : CategoryTheory.Limits.IsLimit C)
      (s : Set C.pt) :
      closure s =
         i,
          (CategoryTheory.ConcreteCategory.hom
                (C.π.app i)) ⁻¹'
            closure
              ((CategoryTheory.ConcreteCategory.hom
                    (C.π.app i)) ''
                s)
Lemma1.1.9
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X = \lim_i X_i be a limit of topological spaces over some index category I and let s \subseteq X be a subset of X. Denote by s_i the image of s in X_i. Then for any morphism f : i \to j in I with transition map \varphi_{f} : X_i \to X_j, we have \varphi_{f}(\overline{s_i}) \subseteq \overline{s_j}.

Lean code for Lemma1.1.91 theorem
  • theoremdefined in Proetale/Topology/Preliminaries/Closure.lean
    complete
    theorem image_closure_image_subset_closure_image.{u_1, u_2, u_3} {I : Type u_1}
      [CategoryTheory.Category.{u_2, u_1} I]
      {F : CategoryTheory.Functor I TopCat}
      (C : CategoryTheory.Limits.Cone F) (s : Set C.pt) {i j : I}
      (f : i  j) :
      (CategoryTheory.ConcreteCategory.hom (F.map f)) ''
          closure
            ((CategoryTheory.ConcreteCategory.hom (C.π.app i)) '' s) 
        closure ((CategoryTheory.ConcreteCategory.hom (C.π.app j)) '' s)
    theorem image_closure_image_subset_closure_image.{u_1,
        u_2, u_3}
      {I : Type u_1}
      [CategoryTheory.Category.{u_2, u_1} I]
      {F : CategoryTheory.Functor I TopCat}
      (C : CategoryTheory.Limits.Cone F)
      (s : Set C.pt) {i j : I} (f : i  j) :
      (CategoryTheory.ConcreteCategory.hom
              (F.map f)) ''
          closure
            ((CategoryTheory.ConcreteCategory.hom
                  (C.π.app i)) ''
              s) 
        closure
          ((CategoryTheory.ConcreteCategory.hom
                (C.π.app j)) ''
            s)
Lemma1.1.10
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let f \colon X \to Y be an embedding of topological spaces. Then f preserves and reflects specializations, i.e. for a, b \in X, a specializes to b if and only if f(a) specializes to f(b).

Lean code for Lemma1.1.101 theorem
  • theoremdefined in Proetale/Mathlib/Topology/Inseparable.lean
    complete
    theorem Topology.IsEmbedding.specializes_iff.{u_2, u_3} {X : Type u_2}
      {Y : Type u_3} [TopologicalSpace X] [TopologicalSpace Y] {f : X  Y}
      (hf : Topology.IsEmbedding f) {x y : X} : f x  f y  x  y
    theorem Topology.IsEmbedding.specializes_iff.{u_2,
        u_3}
      {X : Type u_2} {Y : Type u_3}
      [TopologicalSpace X]
      [TopologicalSpace Y] {f : X  Y}
      (hf : Topology.IsEmbedding f)
      {x y : X} : f x  f y  x  y
Proof for Lemma 1.1.10
uses 0

The only if direction holds for any continuous map. Conversely, if f(a) specializes to f(b), then b \in f^{-1}(\overline{\{f(a)\}}) = \overline{\{a\}}.

Definition1.1.11
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a topological space and Z \subseteq X a subset. The set Z^g = \{ x \in X \mid \exists z \in Z, x \rightsquigarrow z \} is called the generalization of Z in X.

Lean code for Definition1.1.111 definition
  • defdefined in Proetale/Mathlib/Topology/Inseparable.lean
    complete
    def generalizationHull.{u_1} {X : Type u_1} [TopologicalSpace X]
      (s : Set X) : Set X
    def generalizationHull.{u_1} {X : Type u_1}
      [TopologicalSpace X] (s : Set X) : Set X
    The generalization hull of `s` is the smallest set containing `s` that is stable
    under generalization.
    It is equal to the set of points specializing to a point in `s`, see `generalizationHull_eq`. 
Lemma1.1.12
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let Z \subseteq X be a subset of a topological space. Then Z^g is closed under generalization.

Lean code for Lemma1.1.121 theorem
  • theoremdefined in Proetale/Mathlib/Topology/Inseparable.lean
    complete
    theorem stableUnderGeneralization_generalizationHull.{u_1} {X : Type u_1}
      [TopologicalSpace X] (s : Set X) :
      StableUnderGeneralization (generalizationHull s)
    theorem stableUnderGeneralization_generalizationHull.{u_1}
      {X : Type u_1} [TopologicalSpace X]
      (s : Set X) :
      StableUnderGeneralization
        (generalizationHull s)
Proof for Lemma 1.1.12
uses 0

This is immediate from the definition.

The following pure topological lemmas will be used in Lemma 1.7.17 and Lemma 1.5.17.

Definition1.1.13
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Lemma 1.1.14
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Let X be a topological space. Let \pi_0(X) be the set of connected components of X. Let X \to \pi_0(X) be the map which sends x \in X to the connected component of X passing through x. Endow \pi_0(X) with the quotient topology. Then any continuous map X \to Y from X to a totally disconnected space Y factors through \pi_0(X). (Stacks Project, Tag 08ZL)

Lean code for Definition1.1.134 declarations
  • defdefined in Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    def Continuous.connectedComponentsLift.{u, v} {α : Type u} {β : Type v}
      [TopologicalSpace α] [TopologicalSpace β] [TotallyDisconnectedSpace β]
      {f : α  β} (h : Continuous f) : ConnectedComponents α  β
    def Continuous.connectedComponentsLift.{u, v}
      {α : Type u} {β : Type v}
      [TopologicalSpace α]
      [TopologicalSpace β]
      [TotallyDisconnectedSpace β] {f : α  β}
      (h : Continuous f) :
      ConnectedComponents α  β
    The lift to `connectedComponents α` of a continuous map from `α` to a totally disconnected space
    
  • theoremdefined in Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    theorem Continuous.connectedComponentsLift_continuous.{u, v} {α : Type u}
      {β : Type v} [TopologicalSpace α] [TopologicalSpace β]
      [TotallyDisconnectedSpace β] {f : α  β} (h : Continuous f) :
      Continuous h.connectedComponentsLift
    theorem Continuous.connectedComponentsLift_continuous.{u,
        v}
      {α : Type u} {β : Type v}
      [TopologicalSpace α]
      [TopologicalSpace β]
      [TotallyDisconnectedSpace β] {f : α  β}
      (h : Continuous f) :
      Continuous h.connectedComponentsLift
  • theoremdefined in Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    theorem Continuous.connectedComponentsLift_apply_coe.{u, v} {α : Type u}
      {β : Type v} [TopologicalSpace α] [TopologicalSpace β]
      [TotallyDisconnectedSpace β] {f : α  β} (h : Continuous f) (x : α) :
      h.connectedComponentsLift (ConnectedComponents.mk x) = f x
    theorem Continuous.connectedComponentsLift_apply_coe.{u,
        v}
      {α : Type u} {β : Type v}
      [TopologicalSpace α]
      [TopologicalSpace β]
      [TotallyDisconnectedSpace β] {f : α  β}
      (h : Continuous f) (x : α) :
      h.connectedComponentsLift
          (ConnectedComponents.mk x) =
        f x
  • theoremdefined in Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    theorem Continuous.connectedComponentsLift_comp_coe.{u, v} {α : Type u}
      {β : Type v} [TopologicalSpace α] [TopologicalSpace β]
      [TotallyDisconnectedSpace β] {f : α  β} (h : Continuous f) :
      h.connectedComponentsLift  ConnectedComponents.mk = f
    theorem Continuous.connectedComponentsLift_comp_coe.{u,
        v}
      {α : Type u} {β : Type v}
      [TopologicalSpace α]
      [TopologicalSpace β]
      [TotallyDisconnectedSpace β] {f : α  β}
      (h : Continuous f) :
      h.connectedComponentsLift 
          ConnectedComponents.mk =
        f
Lemma1.1.14
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a topological space. Let \pi_0(X) be the topological space of connected components of X. Let Y be a totally disconnected space. If every fiber of X \to Y is connected, then the map \pi_0(X) \to Y is injective.

Lean code for Lemma1.1.141 theorem
  • theoremdefined in Proetale/Mathlib/Topology/Connected/TotallyDisconnected.lean
    complete
    theorem Continuous.connectedComponentsLift_injective.{u_2, u_3} {X : Type u_2}
      [TopologicalSpace X] {Y : Type u_3} [TopologicalSpace Y]
      [TotallyDisconnectedSpace Y] {f : X  Y} (hf : Continuous f)
      (h :  (y : Y), IsPreconnected (f ⁻¹' {y})) :
      Function.Injective hf.connectedComponentsLift
    theorem Continuous.connectedComponentsLift_injective.{u_2,
        u_3}
      {X : Type u_2} [TopologicalSpace X]
      {Y : Type u_3} [TopologicalSpace Y]
      [TotallyDisconnectedSpace Y] {f : X  Y}
      (hf : Continuous f)
      (h :
         (y : Y),
          IsPreconnected (f ⁻¹' {y})) :
      Function.Injective
        hf.connectedComponentsLift
Lemma1.1.15
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Lemma 1.1.16
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L∃∀N

Let X be a topological space. Assume X is quasi-compact, quasi-separated and prespectral. Then for any x \in X the connected component of X containing x is the intersection of all open and closed subsets of X containing x. (Stacks Project, Tag 005F)

Lean code for Lemma1.1.151 theorem
  • theoremdefined in Proetale/Topology/SpectralSpace/ConnectedComponent.lean
    complete
    theorem sInter_isClopen_and_mem_eq_connectedComponent.{u} {X : Type u}
      [TopologicalSpace X] [PrespectralSpace X] [CompactSpace X]
      [QuasiSeparatedSpace X] {x : X} :  U, U = connectedComponent x
    theorem sInter_isClopen_and_mem_eq_connectedComponent.{u}
      {X : Type u} [TopologicalSpace X]
      [PrespectralSpace X] [CompactSpace X]
      [QuasiSeparatedSpace X] {x : X} :
       U, U = connectedComponent x
    [Stacks Tag 005F](https://stacks.math.columbia.edu/tag/005F)
Proof for Lemma 1.1.15
uses 0

Let T be the connected component containing x. Let S = \bigcap_{\alpha \in A} Z_\alpha be the intersection of all open and closed subsets Z_\alpha of X containing x. Note that S is closed in X. Note that any finite intersection of Z_\alpha's is a Z_\alpha. Because T is connected and x \in T we have T \subset Z_\alpha for every Z_\alpha, thus T \subset S. It suffices to show that S is connected. If not, then there exists a disjoint union decomposition S = B \amalg C with B and C open and closed in S. In particular, B and C are closed in X, and so quasi-compact by assumption (1). By assumption (2) there exist quasi-compact opens U, V \subset X with B = S \cap U and C = S \cap V. Then U \cap V \cap S = \emptyset. Hence \bigcap_\alpha U \cap V \cap Z_\alpha = \emptyset. By assumption (3) the intersection U \cap V is quasi-compact. Hence for some \alpha' \in A we have U \cap V \cap Z_{\alpha'} = \emptyset. Since X - (U \cup V) is disjoint from S and closed in X hence quasi-compact, we can use the same argument to see that Z_{\alpha''} \subset U \cup V for some \alpha'' \in A. Then Z_\alpha = Z_{\alpha'} \cap Z_{\alpha''} is contained in U \cup V and disjoint from U \cap V. Hence Z_\alpha = U \cap Z_\alpha \amalg V \cap Z_\alpha is a decomposition into two open pieces, hence U \cap Z_\alpha and V \cap Z_\alpha are open and closed in X. Thus, if x \in B say, then we see that S \subset U \cap Z_\alpha and we conclude that C = \emptyset.

Lemma1.1.16
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a topological space. Assume X is quasi-compact, quasi-separated and prespectral. Then for a subset T \subset X the following are equivalent:

  1. T is an intersection of open and closed subsets of X, and

  2. T is closed in X and is a union of connected components of X.

(Stacks Project, Tag 04PL)

Lean code for Lemma1.1.161 theorem
  • theoremdefined in Proetale/Topology/SpectralSpace/ConnectedComponent.lean
    complete
    theorem isClosed_and_iUnion_connectedComponent_eq_iff.{u} {X : Type u}
      [TopologicalSpace X] [PrespectralSpace X] [CompactSpace X]
      [QuasiSeparatedSpace X] {T : Set X} :
      (IsClosed T   I,  x  I, connectedComponent x = T) 
         J,  U, U = T
    theorem isClosed_and_iUnion_connectedComponent_eq_iff.{u}
      {X : Type u} [TopologicalSpace X]
      [PrespectralSpace X] [CompactSpace X]
      [QuasiSeparatedSpace X] {T : Set X} :
      (IsClosed T 
           I,
             x  I, connectedComponent x =
              T) 
         J,  U, U = T
    [Stacks Tag 04PL](https://stacks.math.columbia.edu/tag/04PL)
Proof for Lemma 1.1.16

It is clear that (a) implies (b). Assume (b). Let x \in X, x \notin T. Let x \in C \subset X be the connected component of X containing x. By Lemma 1.1.15 we see that C = \bigcap V_\alpha is the intersection of all open and closed subsets V_\alpha of X which contain C. In particular, any pairwise intersection V_\alpha \cap V_\beta occurs as a V_\alpha i.e. is still open and closed. As T is a union of connected components of X we see that C \cap T = \emptyset. Hence T \cap \bigcap V_\alpha = \emptyset. Since T is quasi-compact as a closed subset of a quasi-compact space, we deduce that T \cap V_\alpha = \emptyset for some \alpha. For this \alpha we see that U_\alpha = X - V_\alpha is an open and closed subset of X which contains T and not x. The lemma follows.

Lemma1.1.17
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Lemma 1.1.26
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L∃∀N

Let X be a spectral space. Then \pi_0(X) is a profinite space. (Stacks Project, Tag 0906)

Lean code for Lemma1.1.172 theorems
  • theoremdefined in Proetale/Topology/SpectralSpace/ConnectedComponent.lean
    complete
    theorem compactSpace_connectedComponent.{u} {X : Type u} [TopologicalSpace X]
      [CompactSpace X] : CompactSpace (ConnectedComponents X)
    theorem compactSpace_connectedComponent.{u}
      {X : Type u} [TopologicalSpace X]
      [CompactSpace X] :
      CompactSpace (ConnectedComponents X)
  • theoremdefined in Proetale/Topology/SpectralSpace/ConnectedComponent.lean
    complete
    theorem t2Space_connectedComponent.{u} {X : Type u} [TopologicalSpace X]
      [CompactSpace X] [QuasiSeparatedSpace X] [PrespectralSpace X] :
      T2Space (ConnectedComponents X)
    theorem t2Space_connectedComponent.{u}
      {X : Type u} [TopologicalSpace X]
      [CompactSpace X] [QuasiSeparatedSpace X]
      [PrespectralSpace X] :
      T2Space (ConnectedComponents X)
    [Stacks Tag 0906](https://stacks.math.columbia.edu/tag/0906)
Proof for Lemma 1.1.17

We will show that \pi_0(X) is Hausdorff, quasi-compact, and totally disconnected. By Lemma 1.1.15, every connected component of X is the intersection of the open and closed subsets containing it. Since \pi_0(X) is the image of a quasi-compact space, it is also quasi-compact. It is totally disconnected by construction. Let C, D \subset X be distinct connected components of X. Write C = \bigcap_{\alpha} U_\alpha as the intersection of the open and closed subsets of X containing C. Any finite intersection of U_\alpha's is another U_\alpha. Since \bigcap_\alpha U_\alpha \cap D = \emptyset we conclude that U_\alpha \cap D = \emptyset for some \alpha (connected components are closed, thus quasi-compact). Since U_\alpha is open and closed, it is the union of the connected components it contains, i.e., U_\alpha is the inverse image of some open and closed subset V_\alpha \subset \pi_0(X). This proves that the points corresponding to C and D are contained in disjoint open subsets, i.e., \pi_0(X) is Hausdorff.

Lemma1.1.18
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a spectral space. Let Y \subset X be a closed subspace. Then Y is spectral.

Lean code for Lemma1.1.183 theorems
  • theoremdefined in Proetale/Mathlib/Topology/Spectral/Prespectral.lean
    complete
    theorem Topology.IsClosedEmbedding.isOpen_and_isCompact_and_preimage_eq.{u_1,
        u_2}
      {X : Type u_1} {Z : Type u_2} [TopologicalSpace X]
      [TopologicalSpace Z] [PrespectralSpace X] [CompactSpace X] {f : Z  X}
      (hf : Topology.IsClosedEmbedding f) {V : Set Z} (h₁ : IsOpen V)
      (h₂ : IsCompact V) :  U, IsOpen U  IsCompact U  f ⁻¹' U = V
    theorem Topology.IsClosedEmbedding.isOpen_and_isCompact_and_preimage_eq.{u_1,
        u_2}
      {X : Type u_1} {Z : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Z]
      [PrespectralSpace X] [CompactSpace X]
      {f : Z  X}
      (hf : Topology.IsClosedEmbedding f)
      {V : Set Z} (h₁ : IsOpen V)
      (h₂ : IsCompact V) :
       U,
        IsOpen U  IsCompact U  f ⁻¹' U = V
  • theoremdefined in Proetale/Mathlib/Topology/Spectral/Basic.lean
    complete
    theorem Topology.IsClosedEmbedding.spectralSpace.{u_1, u_2} {X : Type u_1}
      {Y : Type u_2} [TopologicalSpace X] [TopologicalSpace Y] {f : X  Y}
      (hf : Topology.IsClosedEmbedding f) [SpectralSpace Y] :
      SpectralSpace X
    theorem Topology.IsClosedEmbedding.spectralSpace.{u_1,
        u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y] {f : X  Y}
      (hf : Topology.IsClosedEmbedding f)
      [SpectralSpace Y] : SpectralSpace X
  • theoremdefined in Proetale/Mathlib/Topology/Spectral/Basic.lean
    complete
    theorem SpectralSpace.of_isClosed.{u_1} (X : Type u_1) [TopologicalSpace X]
      [SpectralSpace X] {C : Set X} [IsClosed C] : SpectralSpace C
    theorem SpectralSpace.of_isClosed.{u_1}
      (X : Type u_1) [TopologicalSpace X]
      [SpectralSpace X] {C : Set X}
      [IsClosed C] : SpectralSpace C
Proof for Lemma 1.1.18
uses 0

The only remaining part in Lean is quasi-separatedness. Suppose that V is open compact in Y, we show that there exists an open compact U in X such that V = U \cap Y. We can find U' in X such that V = U' \cap Y. Write U' = \bigcup_{i \in I} U_i as a union of compact opens, then a finite subset i \in I_0 of U_i already covers V. Take U := \bigcup_{i \in I_0} U_i as desired.

For any compact opens V_1, V_2 \subset Y, there exist compact opens U_1, U_2 \subset X such that V_i = U_i \cap Y. Then V_1 \cap V_2 = (U_1 \cap U_2) \cap Y is still open compact in Y. Here U_1 \cap U_2 is quasi-compact since X is quasi-separated.

Lemma1.1.19
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X and Y be topological spaces. Let (x, y) \in X \times Y be a point. Then \overline{\{(x, y)\}} = \overline{\{x\}} \times \overline{\{y\}}.

Lean code for Lemma1.1.192 theorems
  • theoremdefined in Mathlib/Topology/Constructions/SumProd.lean
    complete
    theorem closure_prod_eq.{u, v} {X : Type u} {Y : Type v} [TopologicalSpace X]
      [TopologicalSpace Y] {s : Set X} {t : Set Y} :
      closure (s ×ˢ t) = closure s ×ˢ closure t
    theorem closure_prod_eq.{u, v} {X : Type u}
      {Y : Type v} [TopologicalSpace X]
      [TopologicalSpace Y] {s : Set X}
      {t : Set Y} :
      closure (s ×ˢ t) =
        closure s ×ˢ closure t
  • theoremdefined in Mathlib/Data/Set/Prod.lean
    complete
    theorem Set.singleton_prod_singleton.{u_1, u_2} {α : Type u_1} {β : Type u_2}
      {a : α} {b : β} : {a} ×ˢ {b} = {(a, b)}
    theorem Set.singleton_prod_singleton.{u_1, u_2}
      {α : Type u_1} {β : Type u_2} {a : α}
      {b : β} : {a} ×ˢ {b} = {(a, b)}
Proof for Lemma 1.1.19
uses 0

It is clear that \overline{\{(x, y)\}} \subseteq \overline{\{x\}} \times \overline{\{y\}}.

If z \notin \overline{\{(x, y)\}}, there exist opens U \subset X, V \subset Y such that z \notin U \times V, thus (x, y) \notin U \times V. Either x \notin U or y \notin V, suppose x \notin U. Then U \cap \overline{\{x\}} = \emptyset, thus U \times V \cap \overline{\{x\}} \times \overline{\{y\}} = \emptyset. This shows that \overline{\{x\}} \times \overline{\{y\}} \subseteq \overline{\{(x, y)\}}.

Lemma1.1.20
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X and Y be spectral spaces. Then the product X \times Y is spectral. (Stacks Project, Tag 0907)

Lean code for Lemma1.1.204 theorems
  • theoremdefined in Proetale/Mathlib/Topology/QuasiSeparated.lean
    complete
    theorem QuasiSeparatedSpace.prod.{u_1, u_2} {α : Type u_1} {β : Type u_2}
      [TopologicalSpace α] [TopologicalSpace β] [QuasiSeparatedSpace α]
      [PrespectralSpace α] [QuasiSeparatedSpace β] [PrespectralSpace β] :
      QuasiSeparatedSpace (α × β)
    theorem QuasiSeparatedSpace.prod.{u_1, u_2}
      {α : Type u_1} {β : Type u_2}
      [TopologicalSpace α]
      [TopologicalSpace β]
      [QuasiSeparatedSpace α]
      [PrespectralSpace α]
      [QuasiSeparatedSpace β]
      [PrespectralSpace β] :
      QuasiSeparatedSpace (α × β)
  • theoremdefined in Proetale/Mathlib/Topology/Sober.lean
    complete
    theorem QuasiSober.prod.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [QuasiSober X]
      [QuasiSober Y] : QuasiSober (X × Y)
    theorem QuasiSober.prod.{u_1, u_2} {X : Type u_1}
      {Y : Type u_2} [TopologicalSpace X]
      [TopologicalSpace Y] [QuasiSober X]
      [QuasiSober Y] : QuasiSober (X × Y)
    The product of two quasi-sober spaces is quasi-sober. 
  • theoremdefined in Proetale/Mathlib/Topology/Spectral/Prespectral.lean
    complete
    theorem PrespectralSpace.prod.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [PrespectralSpace X]
      [PrespectralSpace Y] : PrespectralSpace (X × Y)
    theorem PrespectralSpace.prod.{u_1, u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y]
      [PrespectralSpace X]
      [PrespectralSpace Y] :
      PrespectralSpace (X × Y)
    The product of two prespectral spaces is prespectral. 
  • theoremdefined in Proetale/Mathlib/Topology/Spectral/Basic.lean
    complete
    theorem SpectralSpace.prod.{u_1, u_2} (X : Type u_1) (Y : Type u_2)
      [TopologicalSpace X] [TopologicalSpace Y] [SpectralSpace X]
      [SpectralSpace Y] : SpectralSpace (X × Y)
    theorem SpectralSpace.prod.{u_1, u_2}
      (X : Type u_1) (Y : Type u_2)
      [TopologicalSpace X]
      [TopologicalSpace Y] [SpectralSpace X]
      [SpectralSpace Y] :
      SpectralSpace (X × Y)
    [Stacks Tag 0907](https://stacks.math.columbia.edu/tag/0907)
Proof for Lemma 1.1.20

Let X, Y be spectral spaces. Denote p : X \times Y \to X and q : X \times Y \to Y the projections. We first show that X \times Y is sober. Let Z \subset X \times Y be a closed irreducible subset. Then p(Z) \subset X is irreducible and q(Z) \subset Y is irreducible. Let x \in X be the generic point of the closure of p(Z) and let y \in Y be the generic point of the closure of q(Z). If (x, y) \notin Z, then there exist opens x \in U \subset X, y \in V \subset Y such that Z \cap (U \times V) = \emptyset. Hence Z is contained in (X - U) \times Y \cup X \times (Y - V). Since Z is irreducible, we see that either Z \subset (X - U) \times Y or Z \subset X \times (Y - V). In the first case p(Z) \subset (X - U) and in the second case q(Z) \subset (Y - V). Both cases are absurd as x is in the closure of p(Z) and y is in the closure of q(Z). Thus we conclude that (x, y) \in Z, which means that (x, y) is the generic point of Z (Lemma 1.1.19).

A basis of the topology of X \times Y consists of opens of the form U \times V with U \subset X and V \subset Y quasi-compact open (here we use that X and Y are spectral). Then U \times V is quasi-compact as the product of quasi-compact spaces is quasi-compact. Moreover, any quasi-compact open of X \times Y is a finite union of such quasi-compact rectangles U \times V. It follows that the intersection of two such is again quasi-compact (since X and Y are spectral). This concludes the proof.

Lemma1.1.21
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a topological space. Then X is Hausdorff if and only if the diagonal map \Delta : X \to X \times X is a closed embedding. (Stacks Project, Tag 08ZE)

Lean code for Lemma1.1.211 theorem
  • theoremdefined in Proetale/Mathlib/Topology/Separation/Hausdorff.lean
    complete
    theorem t2Space_iff_diagonal_closed.{u_1} {X : Type u_1} [TopologicalSpace X] :
      T2Space X  IsClosed (Set.range fun x => (x, x))
    theorem t2Space_iff_diagonal_closed.{u_1}
      {X : Type u_1} [TopologicalSpace X] :
      T2Space X 
        IsClosed (Set.range fun x => (x, x))
    [Stacks Tag 08ZE](https://stacks.math.columbia.edu/tag/08ZE)
Lemma1.1.22
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X, Y, and S be topological spaces. Assume that S is Hausdorff. Let f : X \to S and g : Y \to S be continuous maps. The natural map X \times_S Y \to X \times Y is a closed embedding. (Stacks Project, Tag 08ZH)

Lean code for Lemma1.1.221 theorem
  • theoremdefined in Proetale/Mathlib/Topology/Category/TopCat/Limits/Pullbacks.lean
    complete
    theorem TopCat.isClosedEmbedding_pullback_to_prod.{u} {X Y Z : TopCat}
      [T2Space Z] (f : X  Z) (g : Y  Z) :
      Topology.IsClosedEmbedding
        (CategoryTheory.ConcreteCategory.hom
            (CategoryTheory.Limits.prod.lift
              (CategoryTheory.Limits.pullback.fst f g)
              (CategoryTheory.Limits.pullback.snd f g)))
    theorem TopCat.isClosedEmbedding_pullback_to_prod.{u}
      {X Y Z : TopCat} [T2Space Z]
      (f : X  Z) (g : Y  Z) :
      Topology.IsClosedEmbedding
        (CategoryTheory.ConcreteCategory.hom
            (CategoryTheory.Limits.prod.lift
              (CategoryTheory.Limits.pullback.fst
                f g)
              (CategoryTheory.Limits.pullback.snd
                f g)))
    [Stacks Tag 08ZH](https://stacks.math.columbia.edu/tag/08ZH)
Proof for Lemma 1.1.22

X \times_S Y is the inverse image of the image \Delta(S) of the diagonal map \Delta : S \to S \times S. It follows from Lemma 1.1.21 that \Delta(S) is a closed subset.

Lemma1.1.23
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X and Y be topological spaces. If X is spectral (resp. T0, Hausdorff, sober, quasi-separated, quasi-compact, prespectral) and there is a homeomorphism X \cong Y, then Y is spectral (resp. T0, Hausdorff, sober, quasi-separated, quasi-compact, prespectral).

Lean code for Lemma1.1.237 theorems
  • theoremdefined in Proetale/Mathlib/Topology/Spectral/Basic.lean
    complete
    theorem Homeomorph.spectralSpace.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [SpectralSpace X]
      (f : X ≃ₜ Y) : SpectralSpace Y
    theorem Homeomorph.spectralSpace.{u_1, u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y] [SpectralSpace X]
      (f : X ≃ₜ Y) : SpectralSpace Y
  • theoremdefined in Mathlib/Topology/Separation/Basic.lean
    complete
    theorem Homeomorph.t0Space.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [T0Space X] (h : X ≃ₜ Y) :
      T0Space Y
    theorem Homeomorph.t0Space.{u_1, u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y] [T0Space X]
      (h : X ≃ₜ Y) : T0Space Y
  • theoremdefined in Mathlib/Topology/Separation/Hausdorff.lean
    complete
    theorem Homeomorph.t2Space.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [T2Space X] (h : X ≃ₜ Y) :
      T2Space Y
    theorem Homeomorph.t2Space.{u_1, u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y] [T2Space X]
      (h : X ≃ₜ Y) : T2Space Y
  • theoremdefined in Proetale/Mathlib/Topology/Sober.lean
    complete
    theorem Homeomorph.quasiSober.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [QuasiSober X]
      (f : X ≃ₜ Y) : QuasiSober Y
    theorem Homeomorph.quasiSober.{u_1, u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y] [QuasiSober X]
      (f : X ≃ₜ Y) : QuasiSober Y
  • theoremdefined in Proetale/Mathlib/Topology/QuasiSeparated.lean
    complete
    theorem Homeomorph.quasiSeparatedSpace.{u_1, u_2} {α : Type u_1} {β : Type u_2}
      [TopologicalSpace α] [TopologicalSpace β] [QuasiSeparatedSpace α]
      (f : α ≃ₜ β) : QuasiSeparatedSpace β
    theorem Homeomorph.quasiSeparatedSpace.{u_1, u_2}
      {α : Type u_1} {β : Type u_2}
      [TopologicalSpace α]
      [TopologicalSpace β]
      [QuasiSeparatedSpace α] (f : α ≃ₜ β) :
      QuasiSeparatedSpace β
    Quasi-separatedness transfers along homeomorphisms. 
  • theoremdefined in Mathlib/Topology/Homeomorph/Lemmas.lean
    complete
    theorem Homeomorph.compactSpace.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [CompactSpace X]
      (h : X ≃ₜ Y) : CompactSpace Y
    theorem Homeomorph.compactSpace.{u_1, u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y] [CompactSpace X]
      (h : X ≃ₜ Y) : CompactSpace Y
  • theoremdefined in Proetale/Mathlib/Topology/Spectral/Prespectral.lean
    complete
    theorem Homeomorph.prespectralSpace.{u_1, u_2} {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X] [TopologicalSpace Y] [PrespectralSpace X]
      (f : X ≃ₜ Y) : PrespectralSpace Y
    theorem Homeomorph.prespectralSpace.{u_1, u_2}
      {X : Type u_1} {Y : Type u_2}
      [TopologicalSpace X]
      [TopologicalSpace Y]
      [PrespectralSpace X] (f : X ≃ₜ Y) :
      PrespectralSpace Y
    A prespectral space structure transfers along homeomorphisms. 
Lemma1.1.24
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Lemma 1.1.26
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L∃∀N

Let X and Y be spectral spaces. Let S be a Hausdorff topological space. Let f : X \to S and g : Y \to S be continuous maps. Then the fiber product X \times_S Y is spectral.

Lean code for Lemma1.1.2410 theorems
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem T0Space.pullback.{u} {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y] [TopologicalSpace S] [T0Space X] [T0Space Y]
      (f : C(X, S)) (g : C(Y, S)) :
      T0Space
        (CategoryTheory.Limits.pullback (TopCat.ofHom f) (TopCat.ofHom g))
    theorem T0Space.pullback.{u} {X Y S : Type u}
      [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] [T0Space X]
      [T0Space Y] (f : C(X, S))
      (g : C(Y, S)) :
      T0Space
        (CategoryTheory.Limits.pullback
            (TopCat.ofHom f) (TopCat.ofHom g))
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem PrespectralSpace.pullback.{u} {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y] [TopologicalSpace S] [T2Space S]
      [PrespectralSpace X] [PrespectralSpace Y] (f : C(X, S))
      (g : C(Y, S)) :
      PrespectralSpace
        (CategoryTheory.Limits.pullback (TopCat.ofHom f) (TopCat.ofHom g))
    theorem PrespectralSpace.pullback.{u}
      {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] [T2Space S]
      [PrespectralSpace X]
      [PrespectralSpace Y] (f : C(X, S))
      (g : C(Y, S)) :
      PrespectralSpace
        (CategoryTheory.Limits.pullback
            (TopCat.ofHom f) (TopCat.ofHom g))
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem SpectralSpace.pullback.{u} {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y] [TopologicalSpace S] [T2Space S]
      [SpectralSpace X] [SpectralSpace Y] (f : C(X, S)) (g : C(Y, S)) :
      SpectralSpace
        (CategoryTheory.Limits.pullback (TopCat.ofHom f) (TopCat.ofHom g))
    theorem SpectralSpace.pullback.{u}
      {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] [T2Space S]
      [SpectralSpace X] [SpectralSpace Y]
      (f : C(X, S)) (g : C(Y, S)) :
      SpectralSpace
        (CategoryTheory.Limits.pullback
            (TopCat.ofHom f) (TopCat.ofHom g))
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem QuasiSober.pullback.{u} {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y] [TopologicalSpace S] [T2Space S] [QuasiSober X]
      [QuasiSober Y] (f : C(X, S)) (g : C(Y, S)) :
      QuasiSober
        (CategoryTheory.Limits.pullback (TopCat.ofHom f) (TopCat.ofHom g))
    theorem QuasiSober.pullback.{u} {X Y S : Type u}
      [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] [T2Space S]
      [QuasiSober X] [QuasiSober Y]
      (f : C(X, S)) (g : C(Y, S)) :
      QuasiSober
        (CategoryTheory.Limits.pullback
            (TopCat.ofHom f) (TopCat.ofHom g))
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem CompactSpace.pullback.{u} {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y] [TopologicalSpace S] [T2Space S] [CompactSpace X]
      [CompactSpace Y] (f : C(X, S)) (g : C(Y, S)) :
      CompactSpace
        (CategoryTheory.Limits.pullback (TopCat.ofHom f) (TopCat.ofHom g))
    theorem CompactSpace.pullback.{u} {X Y S : Type u}
      [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] [T2Space S]
      [CompactSpace X] [CompactSpace Y]
      (f : C(X, S)) (g : C(Y, S)) :
      CompactSpace
        (CategoryTheory.Limits.pullback
            (TopCat.ofHom f) (TopCat.ofHom g))
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem CategoryTheory.IsPullback.t0Space.{u} {X Y S : Type u}
      [TopologicalSpace X] [TopologicalSpace Y] [TopologicalSpace S]
      {f : C(X, S)} {g : C(Y, S)} {P : Type u} [TopologicalSpace P]
      {f' : C(P, Y)} {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T0Space X] [T0Space Y] : T0Space P
    theorem CategoryTheory.IsPullback.t0Space.{u}
      {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] {f : C(X, S)}
      {g : C(Y, S)} {P : Type u}
      [TopologicalSpace P] {f' : C(P, Y)}
      {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T0Space X] [T0Space Y] : T0Space P
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem CategoryTheory.IsPullback.quasiSober.{u} {X Y S : Type u}
      [TopologicalSpace X] [TopologicalSpace Y] [TopologicalSpace S]
      {f : C(X, S)} {g : C(Y, S)} {P : Type u} [TopologicalSpace P]
      {f' : C(P, Y)} {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [QuasiSober X] [QuasiSober Y] : QuasiSober P
    theorem CategoryTheory.IsPullback.quasiSober.{u}
      {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] {f : C(X, S)}
      {g : C(Y, S)} {P : Type u}
      [TopologicalSpace P] {f' : C(P, Y)}
      {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [QuasiSober X]
      [QuasiSober Y] : QuasiSober P
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem CategoryTheory.IsPullback.compactSpace.{u} {X Y S : Type u}
      [TopologicalSpace X] [TopologicalSpace Y] [TopologicalSpace S]
      {f : C(X, S)} {g : C(Y, S)} {P : Type u} [TopologicalSpace P]
      {f' : C(P, Y)} {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [CompactSpace X] [CompactSpace Y] : CompactSpace P
    theorem CategoryTheory.IsPullback.compactSpace.{u}
      {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] {f : C(X, S)}
      {g : C(Y, S)} {P : Type u}
      [TopologicalSpace P] {f' : C(P, Y)}
      {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [CompactSpace X]
      [CompactSpace Y] : CompactSpace P
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem CategoryTheory.IsPullback.prespectralSpace.{u} {X Y S : Type u}
      [TopologicalSpace X] [TopologicalSpace Y] [TopologicalSpace S]
      {f : C(X, S)} {g : C(Y, S)} {P : Type u} [TopologicalSpace P]
      {f' : C(P, Y)} {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [PrespectralSpace X] [PrespectralSpace Y] :
      PrespectralSpace P
    theorem CategoryTheory.IsPullback.prespectralSpace.{u}
      {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] {f : C(X, S)}
      {g : C(Y, S)} {P : Type u}
      [TopologicalSpace P] {f' : C(P, Y)}
      {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [PrespectralSpace X]
      [PrespectralSpace Y] :
      PrespectralSpace P
  • theoremdefined in Proetale/Topology/Preliminaries/Pullback.lean
    complete
    theorem CategoryTheory.IsPullback.spectralSpace.{u} {X Y S : Type u}
      [TopologicalSpace X] [TopologicalSpace Y] [TopologicalSpace S]
      {f : C(X, S)} {g : C(Y, S)} {P : Type u} [TopologicalSpace P]
      {f' : C(P, Y)} {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [SpectralSpace X] [SpectralSpace Y] : SpectralSpace P
    theorem CategoryTheory.IsPullback.spectralSpace.{u}
      {X Y S : Type u} [TopologicalSpace X]
      [TopologicalSpace Y]
      [TopologicalSpace S] {f : C(X, S)}
      {g : C(Y, S)} {P : Type u}
      [TopologicalSpace P] {f' : C(P, Y)}
      {g' : C(P, X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g') (TopCat.ofHom f')
          (TopCat.ofHom f) (TopCat.ofHom g))
      [T2Space S] [SpectralSpace X]
      [SpectralSpace Y] : SpectralSpace P
Proof for Lemma 1.1.24
Proof uses 4
Proof dependency previews

Note that X \times_S Y is a closed subspace of X \times Y by Lemma 1.1.22. (For subspace, see TopCat.pullbackIsoProdSubtype.) Since X \times Y is spectral (Lemma 1.1.20) it follows that X \times_S Y is spectral (Lemma 1.1.18). Note that we also used Lemma 1.1.23 to translate between categorical constructions and non-categorical constructions.

Lemma1.1.25
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let X be a profinite space. Then X is spectral.

Lean code for Lemma1.1.252 theorems
  • theoremdefined in Proetale/Topology/Preliminaries/Profinite.lean
    complete
    theorem Prespectral.of_profinite.{u_1} {T : Type u_1} [TopologicalSpace T]
      [T2Space T] [CompactSpace T] [TotallyDisconnectedSpace T] :
      PrespectralSpace T
    theorem Prespectral.of_profinite.{u_1}
      {T : Type u_1} [TopologicalSpace T]
      [T2Space T] [CompactSpace T]
      [TotallyDisconnectedSpace T] :
      PrespectralSpace T
  • theoremdefined in Proetale/Topology/Preliminaries/Profinite.lean
    complete
    theorem Spectral.of_profinite.{u_1} {T : Type u_1} [TopologicalSpace T]
      [T2Space T] [CompactSpace T] [TotallyDisconnectedSpace T] :
      SpectralSpace T
    theorem Spectral.of_profinite.{u_1} {T : Type u_1}
      [TopologicalSpace T] [T2Space T]
      [CompactSpace T]
      [TotallyDisconnectedSpace T] :
      SpectralSpace T
Proof for Lemma 1.1.25
uses 0

Since R1 implies sober and Hausdorff implies quasi-separated, it only remains to show that X is prespectral. Write X as an inverse limit of finite discrete topological spaces. The preimages of singletons in every finite discrete space are open and closed subsets and form a topological basis for the topology on X. Thus X is prespectral.

Lemma1.1.26
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Lemma 1.5.17
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L∃∀N

Let X be a spectral space. Let \begin{CD} Y @>>> T \\ @VVV @VVV \\ X @>>> \pi_0(X) \end{CD} be a cartesian diagram in the category of topological spaces with T profinite. Then Y is spectral and the canonical map \pi_0(Y) \to T defined in Definition 1.1.13 is an isomorphism. (Stacks Project, Tag 096C, first part)

Lean code for Lemma1.1.263 theorems
  • theoremdefined in Proetale/Topology/SpectralSpace/ConnectedComponent.lean
    complete
    theorem ConnectedComponents.spectralSpace_of_isPullback.{u} {X : Type u}
      [TopologicalSpace X] [SpectralSpace X] {Y T : Type u}
      [TopologicalSpace Y] [TopologicalSpace T] [CompactSpace T] [T2Space T]
      [TotallyDisconnectedSpace T] {f : C(Y, X)} {g : C(Y, T)}
      {i : C(T, ConnectedComponents X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g) (TopCat.ofHom f)
          (TopCat.ofHom i)
          (TopCat.ofHom
            { toFun := ConnectedComponents.mk, continuous_toFun :=  })) :
      SpectralSpace Y
    theorem ConnectedComponents.spectralSpace_of_isPullback.{u}
      {X : Type u} [TopologicalSpace X]
      [SpectralSpace X] {Y T : Type u}
      [TopologicalSpace Y]
      [TopologicalSpace T] [CompactSpace T]
      [T2Space T] [TotallyDisconnectedSpace T]
      {f : C(Y, X)} {g : C(Y, T)}
      {i : C(T, ConnectedComponents X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g) (TopCat.ofHom f)
          (TopCat.ofHom i)
          (TopCat.ofHom
            { toFun := ConnectedComponents.mk,
              continuous_toFun :=  })) :
      SpectralSpace Y
  • theoremdefined in Proetale/Topology/SpectralSpace/ConnectedComponent.lean
    complete
    theorem ConnectedComponents.lift_bijective_of_isPullback.{u} {X : Type u}
      [TopologicalSpace X] {Y T : Type u} [TopologicalSpace Y]
      [TopologicalSpace T] [CompactSpace T] [T2Space T]
      [TotallyDisconnectedSpace T] {f : C(Y, X)} {g : C(Y, T)}
      {i : C(T, ConnectedComponents X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g) (TopCat.ofHom f)
          (TopCat.ofHom i)
          (TopCat.ofHom
            { toFun := ConnectedComponents.mk, continuous_toFun :=  })) :
      Function.Bijective .connectedComponentsLift
    theorem ConnectedComponents.lift_bijective_of_isPullback.{u}
      {X : Type u} [TopologicalSpace X]
      {Y T : Type u} [TopologicalSpace Y]
      [TopologicalSpace T] [CompactSpace T]
      [T2Space T] [TotallyDisconnectedSpace T]
      {f : C(Y, X)} {g : C(Y, T)}
      {i : C(T, ConnectedComponents X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g) (TopCat.ofHom f)
          (TopCat.ofHom i)
          (TopCat.ofHom
            { toFun := ConnectedComponents.mk,
              continuous_toFun :=  })) :
      Function.Bijective
        .connectedComponentsLift
  • theoremdefined in Proetale/Topology/SpectralSpace/ConnectedComponent.lean
    complete
    theorem ConnectedComponents.isHomeomorph_lift_of_isPullback.{u} {X : Type u}
      [TopologicalSpace X] [SpectralSpace X] {Y T : Type u}
      [TopologicalSpace Y] [TopologicalSpace T] [CompactSpace T] [T2Space T]
      [TotallyDisconnectedSpace T] {f : C(Y, X)} {g : C(Y, T)}
      {i : C(T, ConnectedComponents X)}
      (pb :
        CategoryTheory.IsPullback (TopCat.ofHom g) (TopCat.ofHom f)
          (TopCat.ofHom i)
          (TopCat.ofHom
            { toFun := ConnectedComponents.mk, continuous_toFun :=  })) :
      IsHomeomorph .connectedComponentsLift
    theorem ConnectedComponents.isHomeomorph_lift_of_isPullback.{u}
      {X : Type u} [TopologicalSpace X]
      [SpectralSpace X] {Y T : Type u}
      [TopologicalSpace Y]
      [TopologicalSpace T] [CompactSpace T]
      [T2Space T] [TotallyDisconnectedSpace T]
      {f : C(Y, X)} {g : C(Y, T)}
      {i : C(T, ConnectedComponents X)}
      (pb :
        CategoryTheory.IsPullback
          (TopCat.ofHom g) (TopCat.ofHom f)
          (TopCat.ofHom i)
          (TopCat.ofHom
            { toFun := ConnectedComponents.mk,
              continuous_toFun :=  })) :
      IsHomeomorph .connectedComponentsLift
    [Stacks Tag 096C](https://stacks.math.columbia.edu/tag/096C) (first part)
Proof for Lemma 1.1.26

By Lemma 1.1.25, T is spectral. By Lemma 1.1.17 \pi_0(X) is Hausdorff. By Lemma 1.1.24, Y is spectral. Let Y \to \pi_0(Y) \to T be the canonical factorization in Definition 1.1.13. It is clear that \pi_0(Y) \to T is surjective. The fibres of Y \to T are homeomorphic to the fibres of X \to \pi_0(X). Hence these fibres are connected. It follows that \pi_0(Y) \to T is injective by Lemma 1.1.14. We conclude that \pi_0(Y) \to T is a homeomorphism since it is a bijective map from a quasi-compact space to a Hausdorff space by isHomeomorph_iff_continuous_bijective.

The following pure algebraic lemma will be used in Lemma 1.6.6.

Lemma1.1.27
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.1
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Let A \to B be a ring map which has going down. Let \p \subset A be a prime ideal and let \q \subset B be a prime ideal lying over \p. Assume that there is at most one prime of B above every prime of A. Then the natural map B_{\p B} \to B_{\q} is an isomorphism. (Stacks Project, Tag 00EA, (1) + (2)(a))

Lean code for Lemma1.1.271 theorem
  • theoremdefined in Proetale/Mathlib/RingTheory/Ideal/GoingDown.lean
    complete
    theorem Algebra.HasGoingDown.isLocalization_atPrime_of_subsingleton.{u_1, u_2}
      {R : Type u_1} {S : Type u_2} [CommRing R] [CommRing S] [Algebra R S]
      [Algebra.HasGoingDown R S] (p : Ideal R) (q : Ideal S) [p.IsPrime]
      [q.IsPrime] [q.LiesOver p]
      (h :
         (p : Ideal R) [p.IsPrime],
          Subsingleton { q // q.IsPrime  q.LiesOver p }) :
      IsLocalization (Algebra.algebraMapSubmonoid S p.primeCompl)
        (Localization.AtPrime q)
    theorem Algebra.HasGoingDown.isLocalization_atPrime_of_subsingleton.{u_1,
        u_2}
      {R : Type u_1} {S : Type u_2}
      [CommRing R] [CommRing S] [Algebra R S]
      [Algebra.HasGoingDown R S] (p : Ideal R)
      (q : Ideal S) [p.IsPrime] [q.IsPrime]
      [q.LiesOver p]
      (h :
         (p : Ideal R) [p.IsPrime],
          Subsingleton
            { q //
              q.IsPrime  q.LiesOver p }) :
      IsLocalization
        (Algebra.algebraMapSubmonoid S
          p.primeCompl)
        (Localization.AtPrime q)
    Stacks 00EA, (1) + (2)(a): if `R → S` has going down and there is at most one prime of
    `S` above every prime of `R`, then for every prime `q` of `S` lying over `p`, the natural map
    `S_{pS} → S_q` is an isomorphism, i.e. `Localization.AtPrime q` is the localization of `S` at
    the image of `R \ p`. 
Proof for Lemma 1.1.27
uses 0

It suffices to show that the elements of B - \q are all invertible in B_{\p B}. Suppose the contrary, let x \in B - \q be an element not invertible in B_{\p B}. We can find a prime ideal \q' \subseteq \p B of B containing x. By going down there exists a prime \q'' \subseteq \q lying over \p' = A \cap \q'. By the uniqueness of primes lying over \p' we see that \q' = \q'', which contradicts the fact that x \notin \q.

Definition1.1.28
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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We say A \to B is a local isomorphism if for every prime \mathfrak{q} \subset B there exists a g \in B, g \notin \mathfrak{q} such that A \to B_g induces an open immersion \Spec (B_g) \to \Spec (A). (Stacks Project, Tag 096E (1))

Lean code for Definition1.1.282 definitions
  • class(1 method)defined in Mathlib/RingTheory/LocalIso.lean
    complete
    class Algebra.IsLocalIso.{u_1, u_2} (R : Type u_1) (S : Type u_2)
      [CommSemiring R] [CommSemiring S] [Algebra R S] : Prop
    class Algebra.IsLocalIso.{u_1, u_2}
      (R : Type u_1) (S : Type u_2)
      [CommSemiring R] [CommSemiring S]
      [Algebra R S] : Prop
    An `R`-algebra `S` is a local isomorphism if source locally (in the geometric sense),
    it is a standard open immersion. 

    Methods

    exists_notMem_isStandardOpenImmersion :  (q : Ideal S) [q.IsPrime],  g  q, Algebra.IsStandardOpenImmersion R (Localization.Away g)
  • defdefined in Proetale/Algebra/LocalIso.lean
    complete
    def RingHom.IsLocalIso.{u_3, u_4} {R : Type u_3} {S : Type u_4}
      [CommSemiring R] [CommSemiring S] (f : R →+* S) : Prop
    def RingHom.IsLocalIso.{u_3, u_4}
      {R : Type u_3} {S : Type u_4}
      [CommSemiring R] [CommSemiring S]
      (f : R →+* S) : Prop
    A ring homomorphism is a local isomorphism if source locally (in the geometric sense),
    it is a standard open immersion. 
Definition1.1.29
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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A ring map A \to B identifies local rings if for every prime \mathfrak{q} \subset B the canonical map A_{\varphi^{-1}(\mathfrak{q})} \to B_{\mathfrak{q}} is an isomorphism. (Stacks Project, Tag 096E (2))

Lean code for Definition1.1.291 definition
  • defdefined in Proetale/Algebra/StalkIso.lean
    complete
    def RingHom.BijectiveOnStalks.{u, v} {R : Type u} {S : Type v} [CommRing R]
      [CommRing S] (f : R →+* S) : Prop
    def RingHom.BijectiveOnStalks.{u, v}
      {R : Type u} {S : Type v} [CommRing R]
      [CommRing S] (f : R →+* S) : Prop
    A ring homomorphism `R →+* S` is bijective on stalks if `R_q →+* S_p` is bijective
    for every pair of primes `q = f⁻¹(p)`. 
Lemma1.1.30
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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The map A \to \prod_{i = 1}^{n} A_i identifies local rings, if A \to A_i identifies local rings for all i.

Lean code for Lemma1.1.302 theorems
  • theoremdefined in Proetale/Algebra/StalkIso.lean
    complete
    theorem RingHom.BijectiveOnStalks.pi.{u, v, u_1} {R : Type u} [CommRing R]
      {ι : Type u_1} [Finite ι] {B : ι  Type v} [(i : ι)  CommRing (B i)]
      {f : (i : ι)  R →+* B i} (hf :  (i : ι), (f i).BijectiveOnStalks) :
      (Pi.ringHom f).BijectiveOnStalks
    theorem RingHom.BijectiveOnStalks.pi.{u, v, u_1}
      {R : Type u} [CommRing R] {ι : Type u_1}
      [Finite ι] {B : ι  Type v}
      [(i : ι)  CommRing (B i)]
      {f : (i : ι)  R →+* B i}
      (hf :
         (i : ι), (f i).BijectiveOnStalks) :
      (Pi.ringHom f).BijectiveOnStalks
    A finite product of ring homomorphisms that are bijective on stalks is bijective on stalks,
    provided each factor is bijective on stalks. 
  • theoremdefined in Proetale/Algebra/StalkIso.lean
    complete
    theorem RingHom.BijectiveOnStalks.prod.{u, v} {R : Type u} {S : Type v}
      [CommRing R] [CommRing S] {T : Type v} [CommRing T] {f : R →+* S}
      {g : R →+* T} (hf : f.BijectiveOnStalks) (hg : g.BijectiveOnStalks) :
      (f.prod g).BijectiveOnStalks
    theorem RingHom.BijectiveOnStalks.prod.{u, v}
      {R : Type u} {S : Type v} [CommRing R]
      [CommRing S] {T : Type v} [CommRing T]
      {f : R →+* S} {g : R →+* T}
      (hf : f.BijectiveOnStalks)
      (hg : g.BijectiveOnStalks) :
      (f.prod g).BijectiveOnStalks
    A binary product of ring homomorphisms that are bijective on stalks is bijective on stalks,
    provided each factor is bijective on stalks. 
Lemma1.1.31
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.33
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L∃∀N

Let A \to B and B \to C be ring maps that identify local rings. Then the composition A \to C also identifies local rings.

Lean code for Lemma1.1.311 theorem
  • theoremdefined in Proetale/Algebra/StalkIso.lean
    complete
    theorem RingHom.BijectiveOnStalks.comp.{u, v, u_1} {R : Type u} {S : Type v}
      [CommRing R] [CommRing S] {T : Type u_1} [CommRing T] {f : R →+* S}
      {g : S →+* T} (hf : f.BijectiveOnStalks) (hg : g.BijectiveOnStalks) :
      (g.comp f).BijectiveOnStalks
    theorem RingHom.BijectiveOnStalks.comp.{u, v, u_1}
      {R : Type u} {S : Type v} [CommRing R]
      [CommRing S] {T : Type u_1} [CommRing T]
      {f : R →+* S} {g : S →+* T}
      (hf : f.BijectiveOnStalks)
      (hg : g.BijectiveOnStalks) :
      (g.comp f).BijectiveOnStalks
Lemma1.1.32
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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uses 0used by 1L∃∀N

Let A be a ring and B \to C be an A-algebra map. Suppose both A \to B and A \to C are bijective on stalks. Then B \to C is bijective on stalks. (Stacks Project, Tag 096D)

Lean code for Lemma1.1.322 theorems
  • theoremdefined in Proetale/Algebra/StalkIso.lean
    complete
    theorem Algebra.BijectiveOnStalks.of_comp.{u_1, u_2, u_3} (R : Type u_1)
      (S : Type u_2) (T : Type u_3) [CommRing R] [CommRing S] [CommRing T]
      [Algebra R S] [Algebra S T] [Algebra R T] [IsScalarTower R S T]
      [Algebra.BijectiveOnStalks R S] [Algebra.BijectiveOnStalks R T] :
      Algebra.BijectiveOnStalks S T
    theorem Algebra.BijectiveOnStalks.of_comp.{u_1,
        u_2, u_3}
      (R : Type u_1) (S : Type u_2)
      (T : Type u_3) [CommRing R] [CommRing S]
      [CommRing T] [Algebra R S] [Algebra S T]
      [Algebra R T] [IsScalarTower R S T]
      [Algebra.BijectiveOnStalks R S]
      [Algebra.BijectiveOnStalks R T] :
      Algebra.BijectiveOnStalks S T
    If `R → S → T` is a tower of `R`-algebras such that `R → S` and `R → T` are both bijective
    on stalks, then `S → T` is bijective on stalks. 
  • theoremdefined in Proetale/Algebra/StalkIso.lean
    complete
    theorem RingHom.BijectiveOnStalks.of_comp.{u, v, u_1} {R : Type u} {S : Type v}
      [CommRing R] [CommRing S] {T : Type u_1} [CommRing T] {f : R →+* S}
      {g : S →+* T} (hf : f.BijectiveOnStalks)
      (hgf : (g.comp f).BijectiveOnStalks) : g.BijectiveOnStalks
    theorem RingHom.BijectiveOnStalks.of_comp.{u, v,
        u_1}
      {R : Type u} {S : Type v} [CommRing R]
      [CommRing S] {T : Type u_1} [CommRing T]
      {f : R →+* S} {g : S →+* T}
      (hf : f.BijectiveOnStalks)
      (hgf : (g.comp f).BijectiveOnStalks) :
      g.BijectiveOnStalks
    If `f : R →+* S` and the composition `g.comp f : R →+* T` are both bijective on stalks,
    then `g : S →+* T` is bijective on stalks. 
Proof for Lemma 1.1.32
uses 0

Holds because the same holds for bijective maps of sets.

Definition1.1.33
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Definition 1.1.29
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used by 1XL∃∀N

Let A be a ring and X = \Spec(A). Let \operatorname{ILR}_A denote the category of A-algebras B for which A \to B identifies local rings, and let \operatorname{Top}_X denote the category of topological spaces over X.

Define the functor F \colon \operatorname{ILR}_A \longrightarrow \operatorname{Top}_X by sending B to \Spec(B). (Stacks Project, Tag 096L)

Lemma1.1.34
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Let A be a ring. Set X = \Spec (A). The functor F constructed in Definition 1.1.33, B \longmapsto \Spec (B), from the category of A-algebras B such that A \to B identifies local rings to the category of topological spaces over X is fully faithful. (Stacks Project, Tag 096L)

Proof for Lemma 1.1.34
uses 0

The functor F is a composition of two functors:

  1. The fully faithful functor from the category of A-algebras B for which A \to B identifies local rings to the category of ringed spaces (Y, \mathcal{O}_Y) over X = \Spec(A) satisfying \mathcal{O}_Y = p^{-1}\mathcal{O}_X, where p \colon Y \to X is the structure map.

  2. The functor sending a ringed space to its underlying topological space, and a morphism (f, f^\#) to f.

The second functor is fully faithful because f^\# is always an isomorphism, being given by the canonical identification f^{-1}\mathcal{O}_Y \cong f^{-1}p^{-1}\mathcal{O}_X = q^{-1}\mathcal{O}_X \cong \mathcal{O}_Z, where p \colon Y \to X and q \colon Z \to X are the structure maps.

Definition1.1.35
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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XL∃∀N

Let A be a ring and X = \Spec(A). Let A \to B and A \to C be two A-algebras that identify local rings. As a consequence of Lemma 1.1.34, we have a bijective map F : \Hom_{A\text{-alg}}(B, C) \to \Hom_{\mathrm{Top}_X}(\Spec(C), \Spec(B)) sending f : B \to C to the continuous map \Spec(f) : \Spec(C) \to \Spec(B) induced by f.

Lemma1.1.36
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Let R be a commutative semiring, M a finitely generated R-module, S \subseteq R a submonoid and g \colon M \to M' a localization of M at S. Then M' is the trivial module if and only if there exists t \in S such that t \cdot m = 0 for all m \in M.

Lean code for Lemma1.1.361 theorem
  • theoremdefined in Proetale/Mathlib/Algebra/Module/LocalizedModule/Finiteness.lean
    complete
    theorem IsLocalizedModule.subsingleton_iff_exists_mem_smul_eq_zero.{u_1, u_2,
        u_3}
      {R : Type u_1} [CommSemiring R] {M : Type u_2} [AddCommMonoid M]
      [Module R M] {M' : Type u_3} [AddCommMonoid M'] [Module R M']
      [Module.Finite R M] (S : Submonoid R) (g : M →ₗ[R] M')
      [IsLocalizedModule S g] :
      Subsingleton M'   t  S,  (m : M), t  m = 0
    theorem IsLocalizedModule.subsingleton_iff_exists_mem_smul_eq_zero.{u_1,
        u_2, u_3}
      {R : Type u_1} [CommSemiring R]
      {M : Type u_2} [AddCommMonoid M]
      [Module R M] {M' : Type u_3}
      [AddCommMonoid M'] [Module R M']
      [Module.Finite R M] (S : Submonoid R)
      (g : M →ₗ[R] M')
      [IsLocalizedModule S g] :
      Subsingleton M' 
         t  S,  (m : M), t  m = 0
    For a finitely generated `R`-module `M` and a localization `g : M →ₗ[R] M'`
    of `M` at a submonoid `S ⊆ R`, `M'` is trivial iff a single element of `S`
    annihilates all of `M`. 
Lemma1.1.37
Group: Topological and ring-theoretic preliminaries on w-local spaces and w-local, w-strictly local and w-contractible rings, following Section 2 of Bhatt–Scholze and the Stacks Project. (136)
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Let A = \colim_i A_i be a filtered colimit of A-algebras and let B be an étale A-algebra. Then there exists an i and an étale A_i-algebra B' such that \begin{CD} A_i @>>> B' \\ @VVV @VVV \\ A @>>> B \end{CD} is a pushout diagram.

Proof for Lemma 1.1.37

This follows because every étale algebra is of finite presentation and by possibly enlarging i we can ensure that B' is étale over A_i. The latter step uses Lemma 1.1.36 to find a single index i whose stage trivialises the relevant cotangent / differentials module.