Definition 1.14.1 (Etingof–Gelaki–Nikshych–Ostrik): A quasi-tensor functor
between abelian monoidal categories C and D over a field k. It consists of an
exact (mono- and epi-preserving) faithful functor F equipped with natural
isomorphisms J X Y : F X ⊗ F Y ≅ F (X ⊗ Y) and a unit isomorphism
F (𝟙_ C) ≅ 𝟙_ D.
- F : CategoryTheory.Functor C D
- preservesMono : self.F.PreservesMonomorphisms
- preservesEpi : self.F.PreservesEpimorphisms
- J (X Y : C) : CategoryTheory.MonoidalCategoryStruct.tensorObj (self.F.obj X) (self.F.obj Y) ≅ self.F.obj (CategoryTheory.MonoidalCategoryStruct.tensorObj X Y)
- J_natural_left {X X' : C} (f : X ⟶ X') (Y : C) : CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerRight (self.F.map f) (self.F.obj Y)) (self.J X' Y).hom = CategoryTheory.CategoryStruct.comp (self.J X Y).hom (self.F.map (CategoryTheory.MonoidalCategoryStruct.whiskerRight f Y))
- J_natural_right (X : C) {Y Y' : C} (g : Y ⟶ Y') : CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerLeft (self.F.obj X) (self.F.map g)) (self.J X Y').hom = CategoryTheory.CategoryStruct.comp (self.J X Y).hom (self.F.map (CategoryTheory.MonoidalCategoryStruct.whiskerLeft X g))
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Definition 1.14.1 (Etingof–Gelaki–Nikshych–Ostrik): A tensor functor between
abelian monoidal categories C and D over a field k is an exact faithful
functor F equipped with a monoidal structure (coherent associativity and unit
isomorphisms).
- F : CategoryTheory.Functor C D
- preservesMono : self.F.PreservesMonomorphisms
- preservesEpi : self.F.PreservesEpimorphisms
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Every tensor functor is in particular a quasi-tensor functor: the monoidal
structure provides the natural isomorphisms J and the unit isomorphism.
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Reference abbreviation for Definition 1.14.1: a quasi-tensor functor.
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Reference abbreviation for Definition 1.14.1: a tensor functor.
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A quasi-tensor functor is left exact: its underlying functor preserves monomorphisms.
A quasi-tensor functor is right exact: its underlying functor preserves epimorphisms.
A quasi-tensor functor is faithful.
A quasi-tensor functor preserves the unit object, as recorded by its unit isomorphism.
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A tensor functor is left exact: its underlying functor preserves monomorphisms.
A tensor functor is right exact: its underlying functor preserves epimorphisms.
A tensor functor is faithful.
The unit isomorphism of a tensor functor, derived from its monoidal structure.
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A quasi-tensor functor whose underlying functor carries a monoidal structure upgrades to a tensor functor.
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Definition 1.19.1 (Etingof–Gelaki–Nikshych–Ostrik): A quasi-fiber functor on an
abelian monoidal category C over a field k is a quasi-tensor functor from C
to the category of k-modules.
- F : CategoryTheory.Functor C (ModuleCat k)
- preservesMono : self.F.PreservesMonomorphisms
- preservesEpi : self.F.PreservesEpimorphisms
- J (X Y : C) : CategoryTheory.MonoidalCategoryStruct.tensorObj (self.F.obj X) (self.F.obj Y) ≅ self.F.obj (CategoryTheory.MonoidalCategoryStruct.tensorObj X Y)
- J_natural_left {X X' : C} (f : X ⟶ X') (Y : C) : CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerRight (self.F.map f) (self.F.obj Y)) (self.J X' Y).hom = CategoryTheory.CategoryStruct.comp (self.J X Y).hom (self.F.map (CategoryTheory.MonoidalCategoryStruct.whiskerRight f Y))
- J_natural_right (X : C) {Y Y' : C} (g : Y ⟶ Y') : CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategoryStruct.whiskerLeft (self.F.obj X) (self.F.map g)) (self.J X Y').hom = CategoryTheory.CategoryStruct.comp (self.J X Y).hom (self.F.map (CategoryTheory.MonoidalCategoryStruct.whiskerLeft X g))
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Definition 1.19.1 (Etingof–Gelaki–Nikshych–Ostrik): A fiber functor on an
abelian monoidal category C over a field k is a tensor functor from C to the
category of k-modules.
- F : CategoryTheory.Functor C (ModuleCat k)
- preservesMono : self.F.PreservesMonomorphisms
- preservesEpi : self.F.PreservesEpimorphisms
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Reference abbreviation for Definition 1.19.1: a quasi-fiber functor.
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Reference abbreviation for Definition 1.19.1: a fiber functor.
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A fiber functor on C is in particular a tensor functor from C to the
category of k-modules.
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A fiber functor is in particular a quasi-fiber functor, via its monoidal structure.
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A tensor functor from C to the category of k-modules is a fiber functor on C.
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Exhibit a quasi-fiber functor as a quasi-tensor functor into the category of
k-modules.
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Definition 1.34.1 (Etingof–Gelaki–Nikshych–Ostrik): A quasi-fiber functor QFF
is normalized when the natural isomorphisms J are compatible with the left and
right unit constraints via the unit isomorphism.
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Reference abbreviation for Definition 1.34.1: a normalized quasi-fiber functor.
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Reference abbreviation for Definition 1.34.1.
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Definition 1.34.2 (Etingof–Gelaki–Nikshych–Ostrik): Two quasi-fiber functors
on C are twist-equivalent if they share the same underlying functor.
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The twist isomorphism on QFF₁.F X ⊗ QFF₁.F Y obtained from a twist-equivalence
h : QFF₁.TwistEquivalent QFF₂, comparing the two natural isomorphisms J on
the same underlying functor.
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Reference abbreviation for Definition 1.34.2: twist-equivalence of quasi-fiber functors.
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An object P of an abelian category C is a projective generator if it is
projective and detects zero objects (any X admitting only the zero map from P
must itself be zero).
- proj : CategoryTheory.Projective P
- generates (X : C) : (∀ (f : P ⟶ X), f = 0) → CategoryTheory.Limits.IsZero X
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Every finite abelian k-linear category with enough projectives admits a
projective generator.
A finite rigid k-linear monoidal category over an algebraically closed field
with End(𝟙) ≃ₐ[k] k and a projective generator P admits a fiber functor.
The endomorphism algebra of a fiber functor on a finite rigid k-linear
monoidal category over an algebraically closed field carries a Hopf algebra
structure.
The endomorphism algebra of a fiber functor on a finite rigid k-linear
monoidal category over an algebraically closed field is finite-dimensional.
Every finite-dimensional Hopf algebra H over an algebraically closed field
arises as the endomorphisms of a fiber functor on some finite rigid k-linear
monoidal category.
Any two exact faithful k-linear functors from a finite abelian monoidal
category to the category of k-modules are naturally isomorphic.
Proposition 1.34.7 (Etingof–Gelaki–Nikshych–Ostrik): On a finite abelian
k-linear monoidal category, any two quasi-fiber functors are naturally
isomorphic on the underlying functors; equivalently, a quasi-fiber functor is
unique up to twisting.
Reference abbreviation for Definition 1.14.1: a quasi-tensor functor.
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Reference abbreviation for Definition 1.14.1: a tensor functor.
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Reference abbreviation for Definition 1.14.1.
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Reference abbreviation for Definition 1.19.1: a quasi-fiber functor.
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Reference abbreviation for Definition 1.19.1: a fiber functor.
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Reference abbreviation for Definition 1.19.1.