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Mathlib.Topology.Algebra.Category.ProfiniteGrp.Basic

Category of Profinite Groups #

We say G is a profinite group if it is a topological group which is compact and totally disconnected.

Main definitions and results #

structure ProfiniteGrp :
Type (u_1 + 1)

The category of profinite groups. A term of this type consists of a profinite set with a topological group structure.

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    structure ProfiniteAddGrp :
    Type (u_1 + 1)

    The category of profinite additive groups. A term of this type consists of a profinite set with a topological additive group structure.

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      @[reducible, inline]

      Construct a term of ProfiniteGrp from a type endowed with the structure of a compact and totally disconnected topological group. (The condition of being Hausdorff can be omitted here because totally disconnected implies that {1} is a closed set, thus implying Hausdorff in a topological group.)

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          @[reducible, inline]

          Construct a term of ProfiniteAddGrp from a type endowed with the structure of a compact and totally disconnected topological additive group. (The condition of being Hausdorff can be omitted here because totally disconnected implies that {0} is a closed set, thus implying Hausdorff in a topological additive group.)

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              The type of morphisms in ProfiniteAddGrp.

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                theorem ProfiniteAddGrp.Hom.ext {A B : ProfiniteAddGrp.{u}} {x y : A.Hom B} (hom' : x.hom' = y.hom') :
                x = y

                The type of morphisms in ProfiniteGrp.

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                  theorem ProfiniteGrp.Hom.ext {A B : ProfiniteGrp.{u}} {x y : A.Hom B} (hom' : x.hom' = y.hom') :
                  x = y
                  theorem ProfiniteGrp.Hom.ext_iff {A B : ProfiniteGrp.{u}} {x y : A.Hom B} :
                  x = y x.hom' = y.hom'
                  @[reducible, inline]

                  The underlying ContinuousMonoidHom.

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                      @[reducible, inline]

                      The underlying ContinuousAddMonoidHom.

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                          @[reducible, inline]

                          Typecheck a ContinuousMonoidHom as a morphism in ProfiniteGrp.

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                              theorem ProfiniteGrp.comp_apply {A B C : ProfiniteGrp.{u}} (f : A B) (g : B C) (a : A.toProfinite.toTop) :
                              theorem ProfiniteGrp.hom_ext {A B : ProfiniteGrp.{u}} {f g : A B} (hf : Hom.hom f = Hom.hom g) :
                              f = g
                              theorem ProfiniteAddGrp.hom_ext {A B : ProfiniteAddGrp.{u}} {f g : A B} (hf : Hom.hom f = Hom.hom g) :
                              f = g
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                              theorem ProfiniteGrp.ofHom_hom {A B : ProfiniteGrp.{u}} (f : A B) :
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                              theorem ProfiniteGrp.inv_hom_apply {A B : ProfiniteGrp.{u}} (e : A B) (x : A.toProfinite.toTop) :
                              (Hom.hom e.inv) ((Hom.hom e.hom) x) = x
                              theorem ProfiniteGrp.hom_inv_apply {A B : ProfiniteGrp.{u}} (e : A B) (x : B.toProfinite.toTop) :
                              (Hom.hom e.hom) ((Hom.hom e.inv) x) = x
                              @[simp]
                              theorem ProfiniteGrp.coe_comp {X Y Z : ProfiniteGrp.{u_1}} (f : X Y) (g : Y Z) :
                              @[simp]
                              @[reducible, inline]

                              Construct a term of ProfiniteGrp from a type endowed with the structure of a profinite topological group.

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                                  @[reducible, inline]

                                  Construct a term of ProfiniteAddGrp from a type endowed with the structure of a profinite topological additive group.

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                                      The pi-type of profinite groups is a profinite group.

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                                          The pi-type of profinite additive groups is a profinite additive group.

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                                              A FiniteGrp when given the discrete topology can be considered as a profinite group.

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                                                  A FiniteAddGrp when given the discrete topology can be considered as a profinite additive group.

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                                                      A closed subgroup of a profinite group is profinite.

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                                                          A closed additive subgroup of a profinite additive group is profinite.

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                                                              A topological group that has a ContinuousMulEquiv to a profinite group is profinite.

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                                                                  A topological additive group that has a ContinuousAddEquiv to a profinite additive group is profinite.

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                                                                      Build an isomorphism in the category ProfiniteGrp from a ContinuousMulEquiv between ProfiniteGrps.

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                                                                          The functor mapping a profinite group to its underlying profinite space.

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                                                                            Limits in the category of profinite groups #

                                                                            In this section, we construct limits in the category of profinite groups.

                                                                            TODO #

                                                                            Auxiliary construction to obtain the group structure on the limit of profinite groups.

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                                                                                Auxiliary construction to obtain the additive group structure on the limit of profinite additive groups.

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                                                                                    @[reducible, inline]

                                                                                    The explicit limit cone in ProfiniteGrp.

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                                                                                        @[reducible, inline]

                                                                                        The abbreviation for the limit of ProfiniteGrps.

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                                                                                            theorem ProfiniteGrp.limit_ext {J : Type v} [CategoryTheory.SmallCategory J] (F : CategoryTheory.Functor J ProfiniteGrp.{max v u}) (x y : (limit F).toProfinite.toTop) (hxy : ∀ (j : J), x j = y j) :
                                                                                            x = y
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                                                                                            theorem ProfiniteGrp.limit_mul_val {J : Type v} [CategoryTheory.SmallCategory J] (F : CategoryTheory.Functor J ProfiniteGrp.{max v u}) (x y : (limit F).toProfinite.toTop) (j : J) :
                                                                                            ↑(x * y) j = x j * y j