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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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.
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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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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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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- IndexNotation.OverColor.lift.homToRepHom F m = { hom := ModuleCat.ofHom ↑(IndexNotation.OverColor.lift.linearIsoOfHom F m), comm := ⋯ }
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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 monoidal functor.
This is made manifest in the result
The unit isomorphism between 𝟙_ (Rep k G) and toRep F (𝟙_ (OverColor C))
generated using PiTensorProduct.isEmptyEquiv.
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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.
Equations
- IndexNotation.OverColor.lift.discreteSumEquiv F (Sum.inl val) = LinearEquiv.refl k (Sum.elim (fun (i : X) => ↑(F.obj { as := cX i }).V) (fun (i : Y) => ↑(F.obj { as := cY i }).V) (Sum.inl val))
- IndexNotation.OverColor.lift.discreteSumEquiv F (Sum.inr val) = LinearEquiv.refl k (Sum.elim (fun (i : X) => ↑(F.obj { as := cX i }).V) (fun (i : Y) => ↑(F.obj { as := cY i }).V) (Sum.inr val))
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The equivalence of modules corresponding to the tensor.
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The natural isomorphism corresponding to the tensor.
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The lift of a functor is lax braided.
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The lift of a functor is monoidal.
The lift of a functor is braided.
Equations
- IndexNotation.OverColor.lift.toRepFunc_braidedFunctor F = { toMonoidal := IndexNotation.OverColor.lift.toRepFunc_monoidalFunctor F, braided := ⋯ }
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.
Equations
- IndexNotation.OverColor.lift.repNatTransOfColorApp η X = { hom := ModuleCat.ofHom (PiTensorProduct.map fun (x : X.left) => ModuleCat.Hom.hom (η.app { as := X.hom x }).hom), comm := ⋯ }
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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'.
Equations
- IndexNotation.OverColor.lift.repNatTransOfColor η = { app := IndexNotation.OverColor.lift.repNatTransOfColorApp η, naturality := ⋯ }
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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 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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The lift of a functor is monoidal.
The lift of a functor is lax-braided.
The lift of a functor is braided.
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The natural inclusion of Discrete C into OverColor C.
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- IndexNotation.OverColor.incl = CategoryTheory.Discrete.functor fun (c : C) => IndexNotation.OverColor.mk fun (x : Fin 1) => 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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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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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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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.