Oplax functors #
An oplax functor F between bicategories B and C consists of
- a function between objects
F.obj : B ⟶ C, - a family of functions between 1-morphisms
F.map : (a ⟶ b) → (F.obj a ⟶ F.obj b), - a family of functions between 2-morphisms
F.map₂ : (f ⟶ g) → (F.map f ⟶ F.map g), - a family of 2-morphisms
F.mapId a : F.map (𝟙 a) ⟶ 𝟙 (F.obj a), - a family of 2-morphisms
F.mapComp f g : F.map (f ≫ g) ⟶ F.map f ≫ F.map g, and - certain consistency conditions on them.
Main definitions #
CategoryTheory.OplaxFunctor B C: an oplax functor between bicategoriesBandC, which we denote byB ⥤ᵒᵖᴸ C.CategoryTheory.OplaxFunctor.comp F G: the composition of oplax functors
An oplax functor F between bicategories B and C consists of a function between objects
F.obj, a function between 1-morphisms F.map, and a function between 2-morphisms F.map₂.
Unlike functors between categories, F.map do not need to strictly commute with the composition,
and do not need to strictly preserve the identity. Instead, there are specified 2-morphisms
F.map (𝟙 a) ⟶ 𝟙 (F.obj a) and F.map (f ≫ g) ⟶ F.map f ≫ F.map g.
F.map₂ strictly commute with compositions and preserve the identity. They also preserve the
associator, the left unitor, and the right unitor modulo some adjustments of domains and codomains
of 2-morphisms.
- obj : B → C
- map₂_comp {a b : B} {f g h : a ⟶ b} (η : f ⟶ g) (θ : g ⟶ h) : self.map₂ (CategoryStruct.comp η θ) = CategoryStruct.comp (self.map₂ η) (self.map₂ θ)
The 2-morphism underlying the oplax unity constraint.
- mapComp {a b c : B} (f : a ⟶ b) (g : b ⟶ c) : self.map (CategoryStruct.comp f g) ⟶ CategoryStruct.comp (self.map f) (self.map g)
The 2-morphism underlying the oplax functoriality constraint.
- mapComp_naturality_left {a b c : B} {f f' : a ⟶ b} (η : f ⟶ f') (g : b ⟶ c) : CategoryStruct.comp (self.map₂ (Bicategory.whiskerRight η g)) (self.mapComp f' g) = CategoryStruct.comp (self.mapComp f g) (Bicategory.whiskerRight (self.map₂ η) (self.map g))
Naturality of the oplax functoriality constraint, on the left.
- mapComp_naturality_right {a b c : B} (f : a ⟶ b) {g g' : b ⟶ c} (η : g ⟶ g') : CategoryStruct.comp (self.map₂ (Bicategory.whiskerLeft f η)) (self.mapComp f g') = CategoryStruct.comp (self.mapComp f g) (Bicategory.whiskerLeft (self.map f) (self.map₂ η))
Naturality of the lax functoriality constraint, on the right.
- map₂_associator {a b c d : B} (f : a ⟶ b) (g : b ⟶ c) (h : c ⟶ d) : CategoryStruct.comp (self.map₂ (Bicategory.associator f g h).hom) (CategoryStruct.comp (self.mapComp f (CategoryStruct.comp g h)) (Bicategory.whiskerLeft (self.map f) (self.mapComp g h))) = CategoryStruct.comp (self.mapComp (CategoryStruct.comp f g) h) (CategoryStruct.comp (Bicategory.whiskerRight (self.mapComp f g) (self.map h)) (Bicategory.associator (self.map f) (self.map g) (self.map h)).hom)
Oplax associativity.
- map₂_leftUnitor {a b : B} (f : a ⟶ b) : self.map₂ (Bicategory.leftUnitor f).hom = CategoryStruct.comp (self.mapComp (CategoryStruct.id a) f) (CategoryStruct.comp (Bicategory.whiskerRight (self.mapId a) (self.map f)) (Bicategory.leftUnitor (self.map f)).hom)
Oplax left unity.
- map₂_rightUnitor {a b : B} (f : a ⟶ b) : self.map₂ (Bicategory.rightUnitor f).hom = CategoryStruct.comp (self.mapComp f (CategoryStruct.id b)) (CategoryStruct.comp (Bicategory.whiskerLeft (self.map f) (self.mapId b)) (Bicategory.rightUnitor (self.map f)).hom)
Oplax right unity.
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Notation for a pseudofunctor between bicategories.
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Naturality of the lax functoriality constraint, on the right.
Oplax associativity.
Naturality of the oplax functoriality constraint, on the left.
Naturality of the oplax functoriality constraint, on the left.
Naturality of the lax functoriality constraint, on the right.
Oplax associativity.
Oplax associativity.
Naturality of the lax functoriality constraint, on the right.
Naturality of the oplax functoriality constraint, on the left.
Oplax right unity.
Oplax left unity.
Oplax left unity.
Oplax left unity.
Oplax right unity.
Oplax right unity.
The identity oplax functor.
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More flexible variant of mapId. (See the file Bicategory.Functor.Strict
for applications to strict bicategories.)
Equations
- F.mapId' f hf = CategoryTheory.CategoryStruct.comp (F.map₂ (CategoryTheory.eqToHom ⋯)) (F.mapId b)
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More flexible variant of mapComp. (See Bicategory.Functor.Strict
for applications to strict bicategories.)
Equations
- F.mapComp' f g fg h = CategoryTheory.CategoryStruct.comp (F.map₂ (CategoryTheory.eqToHom ⋯)) (F.mapComp f g)
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Composition of oplax functors.
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A structure on an oplax functor that promotes an oplax functor to a pseudofunctor.
See Pseudofunctor.mkOfOplax.
The isomorphism giving rise to the oplax unity constraint
- mapCompIso {a b c : B} (f : a ⟶ b) (g : b ⟶ c) : F.map (CategoryStruct.comp f g) ≅ CategoryStruct.comp (F.map f) (F.map g)
The isomorphism giving rise to the oplax functoriality constraint
mapIdIsogives rise to the oplax unity constraintmapCompIsogives rise to the oplax functoriality constraint