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PhysLean.Relativity.Tensors.Color.Lift

Lifting functors. #

There is a functor from functors Discrete C ⥤ Rep k G to braided monoidal functors BraidedFunctor (OverColor C) (Rep k G). We call this functor lift. It is a lift in the sense that it is a section of the forgetful functor BraidedFunctor (OverColor C) (Rep k G) ⥤ (Discrete C ⥤ Rep k G).

Functors in Discrete C ⥤ Rep k G form the basic building blocks of tensor structures. The fact that they extend to monoidal functors OverColor C ⥤ Rep k G allows us to interact more generally with tensors.

Takes a homomorphism in Discrete C to an isomorphism built on the same objects.

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    To representation #

    Given an object in OverColor C and a functor F : Discrete C ⥤ Rep k G, we get an object of Rep k G by taking the tensor product of the representations.

    Given an object f : OverColor C and a function F : Discrete C ⥤ Rep k G, the object in Rep k G obtained by taking the tensor product of all colors in f.

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      theorem IndexNotation.OverColor.lift.toRep_ρ_tprod {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) (f : OverColor C) (M : G) (x : (i : f.left) → (F.obj { as := f.hom i }).V) :
      ((toRep F f).ρ M) ((PiTensorProduct.tprod k) x) = (PiTensorProduct.tprod k) fun (i : (CategoryTheory.Functor.id Type).obj f.of.left) => ((F.obj { as := f.hom i }).ρ M) (x i)
      theorem IndexNotation.OverColor.lift.toRep_V_carrier {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) (f : OverColor C) :
      (toRep F f).V = PiTensorProduct k fun (i : f.left) => (F.obj { as := f.hom i }).V

      Hom to representation hom #

      Given a morphism in OverColor C, m : f ⟶ g and a functor F : Discrete C ⥤ Rep k G, we get an morphism in Rep k G between toRep F f and toRep F g by taking the tensor product.

      def IndexNotation.OverColor.lift.linearIsoOfEq {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {c1 c2 : CategoryTheory.Discrete C} (h : c1.as = c2.as) :
      (F.obj c1).V ≃ₗ[k] (F.obj c2).V

      For a function F : Discrete C ⥤ Rep k G, the linear equivalence (F.obj c1).V ≃ₗ[k] (F.obj c2).V induced by an equality of c1 and c2.

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        theorem IndexNotation.OverColor.lift.linearIsoOfEq_comm_ρ {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {c1 c2 : CategoryTheory.Discrete C} (h : c1.as = c2.as) (M : G) (x : (F.obj c1).V) :
        (linearIsoOfEq F h) (((F.obj c1).ρ M) x) = ((F.obj c2).ρ M) ((linearIsoOfEq F h) x)
        def IndexNotation.OverColor.lift.linearIsoOfHom {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {f g : OverColor C} (m : f g) :
        (toRep F f).V ≃ₗ[k] (toRep F g).V

        Given a morphism in OverColor C, m : f ⟶ g and a functor F : Discrete C ⥤ Rep k G, the linear equivalence (toRep F f).V ≃ₗ[k] (toRep F g).V formed by reindexing.

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          theorem IndexNotation.OverColor.lift.linearIsoOfHom_tprod {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {f g : OverColor C} (m : f g) (x : (i : f.left) → (F.obj { as := f.hom i }).V) :
          (linearIsoOfHom F m) ((PiTensorProduct.tprod k) x) = (PiTensorProduct.tprod k) fun (i : g.left) => (linearIsoOfEq F ) (x ((Hom.toEquiv m).symm i))

          Given a morphism in OverColor C, m : f ⟶ g and a functor F : Discrete C ⥤ Rep k G, the morphism (toRep F f) ⟶ (toRep F g) formed by reindexing.

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            theorem IndexNotation.OverColor.lift.homToRepHom_tprod {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {X Y : OverColor C} (p : (i : X.left) → (F.obj { as := X.hom i }).V) (f : X Y) :

            toRepFunc #

            The functions toRep F and homToRepHom F together form a functor.

            The Functor (OverColor C) (Rep k G) from a functor Discrete C ⥤ Rep k G.

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              The braiding of toRepFunc #

              The functor toRepFunc is a braided monodial functor. This is made manifest in the result

              def IndexNotation.OverColor.lift.discreteSumEquiv {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {X Y : Type} {cX : XC} {cY : YC} (i : X Y) :
              Sum.elim (fun (i : X) => (F.obj { as := cX i }).V) (fun (i : Y) => (F.obj { as := cY i }).V) i ≃ₗ[k] (F.obj { as := Sum.elim cX cY i }).V

              An equivalence used in the lemma of μ_tmul_tprod_mk. Identical to μModEquiv except with arguments based on maps instead of elements of OverColor C.

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                theorem IndexNotation.OverColor.lift.μModEquiv_tmul_tprod {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {X Y : OverColor C} (p : (i : X.left) → (F.obj { as := X.hom i }).V) (q : (i : Y.left) → (F.obj { as := Y.hom i }).V) :
                theorem IndexNotation.OverColor.lift.μ_tmul_tprod_mk {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {X Y : Type} {cX : XC} {cY : YC} (p : (i : X) → (F.obj { as := cX i }).V) (q : (i : Y) → (F.obj { as := cY i }).V) :

                The lift of a functor is lax braided.

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                The natural transformation repNatTransOfColor #

                Given two functors F F' : Discrete C ⥤ Rep k G and a natural transformation η : F ⟶ F', we construct a natural transformation repNatTransOfColor : toRepFunc F ⟶ toRepFunc F' by taking the tensor product of the corresponding morphisms in η.

                Given two functors F F' : Discrete C ⥤ Rep k G and a natural transformation η : F ⟶ F', and an X : OverColor C, the (toRepFunc F).obj X ⟶ (toRepFunc F').obj X in Rep k G constructed by the tensor product of the morphisms in η with corresponding color.

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                  Given a natural transformation between F F' : Discrete C ⥤ Rep k G the monoidal natural transformation between toRepFunc F and toRepFunc F'.

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                    The Monoidal structure of repNatTransOfColor #

                    The natural transformation repNatTransOfColor is monoidal, which is made manifest in the results

                    The lift of a natural transformation is monoidal.

                    The functor lift #

                    The functor taking functors in Discrete C ⥤ Rep k G to monoidal functors in BraidedFunctor (OverColor C) (Rep k G), built on the PiTensorProduct.

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                      theorem IndexNotation.OverColor.lift.map_tprod {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) {X Y : OverColor C} (f : X Y) (p : (i : X.left) → (F.obj { as := X.hom i }).V) :

                      The forgetful functor from BraidedFunctor (OverColor C) (Rep k G) to Discrete C ⥤ Rep k G #

                      The natural inclusion of Discrete C into OverColor C.

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                        The forgetful map from BraidedFunctor (OverColor C) (Rep k G) to Discrete C ⥤ Rep k G built on the inclusion incl and forgetting the monoidal structure.

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                          def IndexNotation.OverColor.forgetLiftAppV {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) (c : C) :
                          ((lift.obj F).obj (mk fun (x : Fin 1) => c)).V ≃ₗ[k] (F.obj { as := c }).V

                          The forgetLiftAppV function takes an object c of type C and returns a linear equivalence between the vector space obtained by applying the lift of F and that obtained by applying F. #

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                            @[simp]
                            theorem IndexNotation.OverColor.forgetLiftAppV_symm_apply {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) (c : C) (x : (F.obj { as := c }).V) :
                            (forgetLiftAppV F c).symm x = (PiTensorProduct.tprod k) fun (x_1 : (mk fun (x : Fin 1) => c).left) => x
                            def IndexNotation.OverColor.forgetLiftApp {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) (c : C) :
                            (lift.obj F).obj (mk fun (x : Fin 1) => c) F.obj { as := c }

                            The forgetLiftAppV function takes an object c of type C and returns a isomorphism between the objects obtained by applying the lift of F and that obtained by applying F.

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                              theorem IndexNotation.OverColor.forgetLiftApp_hom_hom_apply_eq {C k : Type} [CommRing k] {G : Type} [Group G] (F : CategoryTheory.Functor (CategoryTheory.Discrete C) (Rep k G)) (c : C) (x : ((lift.obj F).obj (mk fun (x : Fin 1) => c)).V) (y : (F.obj { as := c }).V) :
                              (CategoryTheory.ConcreteCategory.hom (forgetLiftApp F c).hom.hom) x = y x = (PiTensorProduct.tprod k) fun (x : (mk fun (x : Fin 1) => c).left) => y

                              The isomorphism between the representation (lift.obj F).obj (OverColor.mk ![c]) and the representation F.obj (Discrete.mk c). See forgetLiftApp for an alternative version.

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                                The natural isomorphism between lift (C := C) ⋙ forget and Functor.id (Discrete C ⥤ Rep k G).

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