Documentation

Mathlib.Topology.Sets.Compacts

Compact sets #

We define a few types of compact sets in a topological space.

Main Definitions #

For a topological space α,

Compact sets #

structure TopologicalSpace.Compacts (α : Type u_4) [TopologicalSpace α] :
Type u_4

The type of compact sets of a topological space.

  • carrier : Set α

    the carrier set, i.e. the points in this set

  • isCompact' : IsCompact self.carrier
Instances For

    See Note [custom simps projection].

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      Reinterpret a compact as a closed set.

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        @[simp]
        @[simp]
        theorem TopologicalSpace.Compacts.mem_toCloseds {α : Type u_1} [TopologicalSpace α] [T2Space α] {x : α} {s : Compacts α} :
        theorem TopologicalSpace.Compacts.ext {α : Type u_1} [TopologicalSpace α] {s t : Compacts α} (h : s = t) :
        s = t
        theorem TopologicalSpace.Compacts.ext_iff {α : Type u_1} [TopologicalSpace α] {s t : Compacts α} :
        s = t s = t
        @[simp]
        theorem TopologicalSpace.Compacts.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Set α) (h : IsCompact s) :
        { carrier := s, isCompact' := h } = s
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        The type of compact sets is inhabited, with default element the empty set.

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        @[simp]
        theorem TopologicalSpace.Compacts.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : Compacts α) :
        (st) = s t
        @[simp]
        theorem TopologicalSpace.Compacts.coe_inf {α : Type u_1} [TopologicalSpace α] [T2Space α] (s t : Compacts α) :
        (st) = s t
        @[simp]
        theorem TopologicalSpace.Compacts.coe_finset_sup {α : Type u_1} [TopologicalSpace α] {ι : Type u_4} {s : Finset ι} {f : ιCompacts α} :
        (s.sup f) = s.sup fun (i : ι) => (f i)
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        @[simp]
        theorem TopologicalSpace.Compacts.coe_singleton {α : Type u_1} [TopologicalSpace α] (x : α) :
        {x} = {x}
        @[simp]
        theorem TopologicalSpace.Compacts.mem_singleton {α : Type u_1} [TopologicalSpace α] (x y : α) :
        x {y} x = y
        @[simp]
        theorem TopologicalSpace.Compacts.singleton_inj {α : Type u_1} [TopologicalSpace α] {x y : α} :
        {x} = {y} x = y
        def TopologicalSpace.Compacts.map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (K : Compacts α) :

        The image of a compact set under a continuous function.

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          @[simp]
          theorem TopologicalSpace.Compacts.coe_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (s : Compacts α) :
          (Compacts.map f hf s) = f '' s
          @[simp]
          theorem TopologicalSpace.Compacts.map_comp {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : βγ) (g : αβ) (hf : Continuous f) (hg : Continuous g) (K : Compacts α) :
          Compacts.map (f g) K = Compacts.map f hf (Compacts.map g hg K)
          @[simp]
          theorem TopologicalSpace.Compacts.map_singleton {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (x : α) :
          Compacts.map f hf {x} = {f x}

          A homeomorphism induces an equivalence on compact sets, by taking the image.

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            @[simp]
            theorem TopologicalSpace.Compacts.equiv_apply {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : α ≃ₜ β) (K : Compacts α) :
            (Compacts.equiv f) K = Compacts.map f K
            @[simp]
            theorem TopologicalSpace.Compacts.equiv_symm_apply {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : α ≃ₜ β) (K : Compacts β) :
            @[simp]
            theorem TopologicalSpace.Compacts.equiv_trans {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : α ≃ₜ β) (g : β ≃ₜ γ) :
            theorem TopologicalSpace.Compacts.coe_equiv_apply_eq_preimage {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : α ≃ₜ β) (K : Compacts α) :
            ((Compacts.equiv f) K) = f.symm ⁻¹' K

            The image of a compact set under a homeomorphism can also be expressed as a preimage.

            The product of two TopologicalSpace.Compacts, as a TopologicalSpace.Compacts in the product space.

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            @[reducible, inline, deprecated "Use `K ×ˢ L` instead" (since := "2025-11-15")]
            abbrev TopologicalSpace.Compacts.prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : Compacts α) (L : Compacts β) :
            Compacts (α × β)

            The product of two TopologicalSpace.Compacts, as a TopologicalSpace.Compacts in the product space.

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              @[simp]
              theorem TopologicalSpace.Compacts.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : Compacts α) (L : Compacts β) :
              ↑(K ×ˢ L) = K ×ˢ L
              @[simp]
              theorem TopologicalSpace.Compacts.singleton_prod_singleton {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (x : α) (y : β) :

              Nonempty compact sets #

              The type of nonempty compact sets of a topological space.

              Instances For

                See Note [custom simps projection].

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                  Reinterpret a nonempty compact as a closed set.

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                    theorem TopologicalSpace.NonemptyCompacts.ext {α : Type u_1} [TopologicalSpace α] {s t : NonemptyCompacts α} (h : s = t) :
                    s = t
                    @[simp]
                    theorem TopologicalSpace.NonemptyCompacts.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Compacts α) (h : s.carrier.Nonempty) :
                    { toCompacts := s, nonempty' := h } = s
                    @[simp]
                    theorem TopologicalSpace.NonemptyCompacts.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : NonemptyCompacts α) :
                    (st) = s t
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                    @[simp]
                    @[simp]
                    @[simp]

                    In an inhabited space, the type of nonempty compact subsets is also inhabited, with default element the singleton set containing the default element.

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                    def TopologicalSpace.NonemptyCompacts.map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (K : NonemptyCompacts α) :

                    The image of a nonempty compact set under a continuous function.

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                      @[simp]
                      theorem TopologicalSpace.NonemptyCompacts.coe_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (s : NonemptyCompacts α) :
                      (NonemptyCompacts.map f hf s) = f '' s
                      theorem TopologicalSpace.NonemptyCompacts.map_comp {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : βγ) (g : αβ) (hf : Continuous f) (hg : Continuous g) (K : NonemptyCompacts α) :
                      @[simp]
                      theorem TopologicalSpace.NonemptyCompacts.map_singleton {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (x : α) :

                      The product of two TopologicalSpace.NonemptyCompacts, as a TopologicalSpace.NonemptyCompacts in the product space.

                      Equations
                      • One or more equations did not get rendered due to their size.
                      @[reducible, inline, deprecated "Use `K ×ˢ L` instead" (since := "2025-11-15")]

                      The product of two TopologicalSpace.NonemptyCompacts, as a TopologicalSpace.NonemptyCompacts in the product space.

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                        @[simp]
                        theorem TopologicalSpace.NonemptyCompacts.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : NonemptyCompacts α) (L : NonemptyCompacts β) :
                        ↑(K ×ˢ L) = K ×ˢ L
                        @[simp]

                        Positive compact sets #

                        The type of compact sets with nonempty interior of a topological space. See also TopologicalSpace.Compacts and TopologicalSpace.NonemptyCompacts.

                        Instances For

                          See Note [custom simps projection].

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                            Reinterpret a positive compact as a nonempty compact.

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                              theorem TopologicalSpace.PositiveCompacts.ext {α : Type u_1} [TopologicalSpace α] {s t : PositiveCompacts α} (h : s = t) :
                              s = t
                              @[simp]
                              theorem TopologicalSpace.PositiveCompacts.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Compacts α) (h : (interior s.carrier).Nonempty) :
                              { toCompacts := s, interior_nonempty' := h } = s
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                              @[simp]
                              theorem TopologicalSpace.PositiveCompacts.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : PositiveCompacts α) :
                              (st) = s t
                              def TopologicalSpace.PositiveCompacts.map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (hf' : IsOpenMap f) (K : PositiveCompacts α) :

                              The image of a positive compact set under a continuous open map.

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                                @[simp]
                                theorem TopologicalSpace.PositiveCompacts.coe_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (hf' : IsOpenMap f) (s : PositiveCompacts α) :
                                (PositiveCompacts.map f hf hf' s) = f '' s
                                theorem TopologicalSpace.PositiveCompacts.map_comp {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : βγ) (g : αβ) (hf : Continuous f) (hg : Continuous g) (hf' : IsOpenMap f) (hg' : IsOpenMap g) (K : PositiveCompacts α) :
                                theorem exists_positiveCompacts_subset {α : Type u_1} [TopologicalSpace α] [LocallyCompactSpace α] {U : Set α} (ho : IsOpen U) (hn : U.Nonempty) :

                                In a nonempty locally compact space, there exists a compact set with nonempty interior.

                                The product of two TopologicalSpace.PositiveCompacts, as a TopologicalSpace.PositiveCompacts in the product space.

                                Equations
                                • One or more equations did not get rendered due to their size.
                                @[reducible, inline, deprecated "Use `K ×ˢ L` instead" (since := "2025-11-15")]

                                The product of two TopologicalSpace.PositiveCompacts, as a TopologicalSpace.PositiveCompacts in the product space.

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                                  @[simp]
                                  theorem TopologicalSpace.PositiveCompacts.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : PositiveCompacts α) (L : PositiveCompacts β) :
                                  ↑(K ×ˢ L) = K ×ˢ L

                                  Compact open sets #

                                  The type of compact open sets of a topological space. This is useful in non-Hausdorff contexts, in particular spectral spaces.

                                  Instances For

                                    See Note [custom simps projection].

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                                      Reinterpret a compact open as an open.

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                                        Reinterpret a compact open as a clopen.

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                                          theorem TopologicalSpace.CompactOpens.ext {α : Type u_1} [TopologicalSpace α] {s t : CompactOpens α} (h : s = t) :
                                          s = t
                                          theorem TopologicalSpace.CompactOpens.ext_iff {α : Type u_1} [TopologicalSpace α] {s t : CompactOpens α} :
                                          s = t s = t
                                          @[simp]
                                          theorem TopologicalSpace.CompactOpens.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Compacts α) (h : IsOpen s.carrier) :
                                          { toCompacts := s, isOpen' := h } = s
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                                          @[simp]
                                          theorem TopologicalSpace.CompactOpens.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : CompactOpens α) :
                                          (st) = s t
                                          @[simp]
                                          theorem TopologicalSpace.CompactOpens.coe_finsetSup {α : Type u_1} [TopologicalSpace α] {ι : Type u_4} {f : ιCompactOpens α} {s : Finset ι} :
                                          (s.sup f) = is, (f i)
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                                          @[simp]
                                          theorem TopologicalSpace.CompactOpens.coe_inf {α : Type u_1} [TopologicalSpace α] [QuasiSeparatedSpace α] (s t : CompactOpens α) :
                                          (st) = s t
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                                          @[simp]
                                          theorem TopologicalSpace.CompactOpens.coe_sdiff {α : Type u_1} [TopologicalSpace α] [T2Space α] (s t : CompactOpens α) :
                                          ↑(s \ t) = s \ t
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                                          @[simp]
                                          @[simp]
                                          theorem TopologicalSpace.CompactOpens.coe_himp {α : Type u_1} [TopologicalSpace α] [CompactSpace α] [T2Space α] (s t : CompactOpens α) :
                                          ↑(s t) = s t
                                          def TopologicalSpace.CompactOpens.map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (hf' : IsOpenMap f) (s : CompactOpens α) :

                                          The image of a compact open under a continuous open map.

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                                            @[simp]
                                            theorem TopologicalSpace.CompactOpens.toCompacts_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (hf' : IsOpenMap f) (s : CompactOpens α) :
                                            (map f hf hf' s).toCompacts = Compacts.map f hf s.toCompacts
                                            @[deprecated TopologicalSpace.CompactOpens.toCompacts_map (since := "2025-11-13")]
                                            theorem TopologicalSpace.CompactOpens.map_toCompacts {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (hf' : IsOpenMap f) (s : CompactOpens α) :
                                            (map f hf hf' s).toCompacts = Compacts.map f hf s.toCompacts

                                            Alias of TopologicalSpace.CompactOpens.toCompacts_map.

                                            @[simp]
                                            theorem TopologicalSpace.CompactOpens.coe_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (hf' : IsOpenMap f) (s : CompactOpens α) :
                                            (map f hf hf' s) = f '' s
                                            @[simp]
                                            theorem TopologicalSpace.CompactOpens.map_id {α : Type u_1} [TopologicalSpace α] (K : CompactOpens α) :
                                            map id K = K
                                            theorem TopologicalSpace.CompactOpens.map_comp {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : βγ) (g : αβ) (hf : Continuous f) (hg : Continuous g) (hf' : IsOpenMap f) (hg' : IsOpenMap g) (K : CompactOpens α) :
                                            map (f g) K = map f hf hf' (map g hg hg' K)

                                            The product of two TopologicalSpace.CompactOpens, as a TopologicalSpace.CompactOpens in the product space.

                                            Equations
                                            • One or more equations did not get rendered due to their size.
                                            @[reducible, inline, deprecated "Use `K ×ˢ L` instead" (since := "2025-11-15")]

                                            The product of two TopologicalSpace.CompactOpens, as a TopologicalSpace.CompactOpens in the product space.

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                                              @[simp]
                                              theorem TopologicalSpace.CompactOpens.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : CompactOpens α) (L : CompactOpens β) :
                                              ↑(K ×ˢ L) = K ×ˢ L