Documentation

LeanPool.RegtsSevenster.RS.Classical.Deligne.Doubling

The ℤ/2-graded doubling of a category #

Deligne 2.11's device: the category of super-objects over an ambient category A. An object is a pair of objects of A, the even and odd components; a morphism is a pair of component morphisms. The graded tensor product mixes the components in the usual super pattern, the braiding carries the Koszul sign -1 on the odd⊗odd block, and the odd copy of the unit provides an odd invertible object — exactly the hypothesis pair of Deligne 2.9 — to a category that may lack one.

This module mirrors, at the abstract level, the concrete SuperVect construction of RS/Definitions.lean: the same component bookkeeping, with binary biproducts in place of products of vector spaces.

The monoidal coherences are not proved by hand: the summing functor Doubled A ⥤ A, X ↦ X.even ⊞ X.odd, is faithful, and CategoryTheory.Monoidal.induced transports the pentagon and triangle from A along it. The braiding coherences, which the Koszul sign prevents from transporting, are discharged by componentwise matrix checks against the distributor calculus set up in the Distributors section.

structure RS.Doubled (A : Type u) :

A super-object over A: a pair of objects of A, thought of as the even and odd graded components.

  • even : A

    The even component.

  • odd : A

    The odd component.

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    A morphism of super-objects: a pair of component morphisms, preserving the grading.

    • even : X.even ⟶ Y.even

      The even component of the morphism.

    • odd : X.odd ⟶ Y.odd

      The odd component of the morphism.

    Instances For
      theorem RS.Doubled.Hom.ext_iff {A : Type u} {inst✝ : CategoryTheory.Category.{v, u} A} {X Y : Doubled A} {x y : X.Hom Y} :
      x = y ↔ x.even = y.even ∧ x.odd = y.odd
      theorem RS.Doubled.Hom.ext {A : Type u} {inst✝ : CategoryTheory.Category.{v, u} A} {X Y : Doubled A} {x y : X.Hom Y} (even : x.even = y.even) (odd : x.odd = y.odd) :
      x = y
      @[instance_reducible]

      Super-objects form a category with componentwise identities and composition.

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      The even component of a morphism of super-objects.

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        def RS.Doubled.oddHom {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} (f : X ⟶ Y) :
        X.odd ⟶ Y.odd

        The odd component of a morphism of super-objects.

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          theorem RS.Doubled.hom_ext {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} {f g : X ⟶ Y} (he : evenHom f = evenHom g) (ho : oddHom f = oddHom g) :
          f = g

          Morphisms of super-objects agreeing in both components are equal.

          def RS.Doubled.homMk {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} (fe : X.even ⟶ Y.even) (fo : X.odd ⟶ Y.odd) :
          X ⟶ Y

          A morphism of super-objects from a pair of component morphisms.

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            @[simp]
            theorem RS.Doubled.evenHom_homMk {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} (fe : X.even ⟶ Y.even) (fo : X.odd ⟶ Y.odd) :
            evenHom (homMk fe fo) = fe
            @[simp]
            theorem RS.Doubled.oddHom_homMk {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} (fe : X.even ⟶ Y.even) (fo : X.odd ⟶ Y.odd) :
            oddHom (homMk fe fo) = fo
            def RS.Doubled.isoMk {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} (e : X.even ≅ Y.even) (o : X.odd ≅ Y.odd) :
            X ≅ Y

            An isomorphism of super-objects from a pair of component isomorphisms.

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              @[simp]
              theorem RS.Doubled.isoMk_inv {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} (e : X.even ≅ Y.even) (o : X.odd ≅ Y.odd) :
              (isoMk e o).inv = homMk e.inv o.inv
              @[simp]
              theorem RS.Doubled.isoMk_hom {A : Type u} [CategoryTheory.Category.{v, u} A] {X Y : Doubled A} (e : X.even ≅ Y.even) (o : X.odd ≅ Y.odd) :
              (isoMk e o).hom = homMk e.hom o.hom
              @[instance_reducible]

              The componentwise zero morphism.

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              Componentwise addition of morphisms.

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              Componentwise negation of morphisms.

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              The componentwise additive group of morphisms.

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              The doubling of a preadditive category is preadditive, componentwise.

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              A super-object with two zero components is a zero object.

              The doubling of a category with a zero object has a zero object, with both components zero.

              @[instance_reducible]

              The componentwise ℂ-module of morphisms.

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              The doubling of a ℂ-linear category is ℂ-linear, componentwise.

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              @[reducible, inline]

              The graded tensor product of super-objects: parities add, so each component of the product is a biproduct of two mixed blocks.

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                noncomputable def RS.Doubled.tensorHom {A : Type u} [CategoryTheory.Category.{v, u} A] [CategoryTheory.MonoidalCategory A] [CategoryTheory.Preadditive A] [CategoryTheory.Limits.HasBinaryBiproducts A] {X₁ Y₁ X₂ Y₂ : Doubled A} (f : X₁ ⟶ Y₁) (g : X₂ ⟶ Y₂) :
                X₁.tensorObj X₂ ⟶ Y₁.tensorObj Y₂

                The graded tensor product of morphisms, blockwise.

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                  Left whiskering of super-objects, blockwise.

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                    Right whiskering of super-objects, blockwise.

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                      The even component of the associator: each of the four parity blocks re-associates through A's associator and is routed to the matching block of the right-nested product.

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                        The odd component of the associator.

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                          @[reducible, inline]

                          The summing functor X ↦ X.even ⊞ X.odd. It is faithful, and the monoidal coherences of the doubling are induced along it.

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                            The summing functor is faithful: both components are recovered as matrix entries.

                            @[reducible, inline]

                            The monoidal unit of the doubling: the unit of A in even degree, the zero object in odd degree.

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                              Collapse of a unit block against a zero block, in the shape of the left unitor components.

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                                Collapse of a unit block against a zero block, in the shape of the even right unitor component.

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                                  Collapse of a unit block against a zero block, in the shape of the odd right unitor component.

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                                    @[instance_reducible]

                                    The monoidal skeleton of the doubling: graded tensor product, unit (𝟙_ A, 0), blockwise structural isomorphisms.

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                                    Components of the monoidal notation #

                                    The multiplicative comparison of the summing functor: double distribution followed by the parity shuffle.

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                                      The inducing data exhibiting the graded structural morphisms as the images of A's structural morphisms under the parity distributors.

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                                        The doubling of a monoidal preadditive category is monoidal preadditive, componentwise. Each component equation is restated (show) with its objects in literal biproduct form, so that the ambient simp lemmas apply.

                                        The even component of the Koszul braiding: A's braiding on each parity block, with the sign -1 on the odd⊗odd block.

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                                          The odd component of the Koszul braiding: the two mixed blocks swap through A's braiding, with no sign.

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                                            @[instance_reducible]

                                            The doubling of a symmetric category is braided, with the Koszul-signed braiding.

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                                            The even embedding X ↦ (X, 0).

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                                              @[reducible, inline]

                                              The odd unit: the unit of A placed in odd degree. Together with oddUnitSq and braiding_oddUnit this is exactly the invertible odd object required by Deligne 2.9.

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                                                The componentwise binary bicone on a pair of super-objects.

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                                                  Every super-object is the biproduct of its even part and the odd-unit twist of its odd part: the decomposition through which Schur-vanishing transports from A to the doubling.

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                                                    The componentwise kernel fork of a morphism of super-objects.

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                                                      The componentwise kernel fork is limiting.

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                                                        The componentwise cokernel cofork of a morphism of super-objects.

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                                                          The componentwise cokernel cofork is colimiting.

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                                                            A morphism of super-objects whose two components are isomorphisms is an isomorphism.

                                                            @[reducible]

                                                            Componentwise exact pairings pair the doubled objects: the evaluations and coevaluations act blockwise on matching parities, and the odd components vanish.

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                                                              @[instance_reducible]

                                                              The doubling of a right rigid category is right rigid, with componentwise duals.

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                                                              The doubling of a left rigid category is left rigid, with componentwise duals.

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