Left actions from a monoidal category on a category #
Given a monoidal category C, and a category D, we define a left action of
C on D as the data of an object c ⊙ₗ d of D for every
c : C and d : D, as well as the data required to turn - ⊙ₗ - into
a bifunctor, along with structure natural isomorphisms
(- ⊗ -) ⊙ₗ - ≅ - ⊙ₗ - ⊙ₗ - and 𝟙_ C ⊙ₗ - ≅ -, subject to coherence conditions.
References #
- [Janelidze, G, and Kelly, G.M., A note on actions of a monoidal category][JanelidzeKelly2001]
TODOs/Projects #
- Equivalence between actions of
ConDand pseudofunctors from the classifying bicategory ofCtoCat. - Right actions
- Functors that respects left actions.
- Left actions as monoidal functors C ⥤ (D ⥤ D)ᴹᵒᵖ.
- Action of
(C ⥤ C)onC. - Modules in
Dover a monoid object inC. Equivalence withMod_whenDisC. - Given a monad
MonC, equivalence betweenAlgebra M, and modules inConM.toMon : Mon_ (C ⥤ C). - Canonical action of
Type uonu-small cocomplete categories via the copower.
A class that carries the non-Prop data required to define a left action of a
monoidal category C on a category D, to set up notations.
- actionObj : C → D → D
The left action on objects. This is denoted
c ⊙ₗ d. The left action of a map
f : c ⟶ c'inCon an objectdinD. If we are to consider the action as a functorΑ : C ⥤ D ⥤ D, this is (Α.map f).app d. This is denotedf ⊵ₗ d`The action of an object
c : Con a mapf : d ⟶ d'inD. If we are to consider the action as a functorΑ : C ⥤ D ⥤ D, this is (Α.obj c).map f. This is denotedc ⊴ₗ f`.The action of a pair of maps
f : c ⟶ c'andd ⟶ d'. By default, this is defined in terms ofactionHomLeftandactionHomRight.The structural isomorphism
(c ⊗ c') ⊙ₗ d ≅ c ⊙ₗ (c' ⊙ₗ d).The structural isomorphism between
𝟙_ C ⊙ₗ dandd.
Instances
Notation for actionObj, the action of C on D.
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Notation for actionHomLeft, the action of C on morphisms in D.
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Notation for actionHomRight, the action of morphism in C on D.
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Notation for actionHom, the bifunctorial action of morphisms in C and
D on - ⊙ₗ -.
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Notation for actionAssocIso, the structural isomorphism
- ⊗ - ⊙ₗ - ≅ - ⊙ₗ - ⊙ₗ -.
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- CategoryTheory.MonoidalCategory.MonoidalLeftAction.termαₗ = Lean.ParserDescr.node `CategoryTheory.MonoidalCategory.MonoidalLeftAction.termαₗ 1024 (Lean.ParserDescr.symbol "αₗ ")
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Notation for actionUnitIso, the structural isomorphism 𝟙_ C ⊙ₗ - ≅ -.
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- CategoryTheory.MonoidalCategory.MonoidalLeftAction.«termλₗ» = Lean.ParserDescr.node `CategoryTheory.MonoidalCategory.MonoidalLeftAction.«termλₗ» 1024 (Lean.ParserDescr.symbol "λₗ ")
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Notation for actionUnitIso, the structural isomorphism 𝟙_ C ⊙ₗ - ≅ -,
allowing one to specify the acting category.
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A MonoidalLeftAction C D is is the data of:
- For every object
c : Candd : D, an objectc ⊙ₗ dofD. - For every morphism
f : (c : C) ⟶ c'and everyd : D, a morphismf ⊵ₗ d : c ⊙ₗ d ⟶ c' ⊙ₗ d. - For every morphism
f : (d : D) ⟶ d'and everyc : C, a morphismc ⊴ₗ f : c ⊙ₗ d ⟶ c ⊙ₗ d'. - For every pair of morphisms
f : (c : C) ⟶ c'andf : (d : D) ⟶ d', a morphismf ⊙ₗ f' : c ⊙ₗ d ⟶ c' ⊙ₗ d'. - A structure isomorphism
αₗ c c' d : c ⊗ c' ⊙ₗ d ≅ c ⊙ₗ c' ⊙ₗ d. - A structure isomorphism
λₗ d : (𝟙_ C) ⊙ₗ d ≅ d. Furthermore, we require identities that turn- ⊙ₗ -into a bifunctor, ensure naturality ofαₗandλₗ, and ensure compatibilies with the associator and unitor isomorphisms inC.
- actionObj : C → D → D
- actionHom_def {c c' : C} {d d' : D} (f : c ⟶ c') (g : d ⟶ d') : actionHom f g = CategoryStruct.comp (actionHomLeft f d) (actionHomRight c' g)
- actionHomRight_id (c : C) (d : D) : actionHomRight c (CategoryStruct.id d) = CategoryStruct.id (actionObj c d)
- id_actionHomLeft (c : C) (d : D) : actionHomLeft (CategoryStruct.id c) d = CategoryStruct.id (actionObj c d)
- actionHom_comp {c c' c'' : C} {d d' d'' : D} (f₁ : c ⟶ c') (f₂ : c' ⟶ c'') (g₁ : d ⟶ d') (g₂ : d' ⟶ d'') : actionHom (CategoryStruct.comp f₁ f₂) (CategoryStruct.comp g₁ g₂) = CategoryStruct.comp (actionHom f₁ g₁) (actionHom f₂ g₂)
- actionAssocIso_hom_naturality {c₁ c₂ c₃ c₄ : C} {d₁ d₂ : D} (f : c₁ ⟶ c₂) (g : c₃ ⟶ c₄) (h : d₁ ⟶ d₂) : CategoryStruct.comp (actionHom (tensorHom f g) h) (actionAssocIso c₂ c₄ d₂).hom = CategoryStruct.comp (actionAssocIso c₁ c₃ d₁).hom (actionHom f (actionHom g h))
- actionUnitIso_hom_naturality {d d' : D} (f : d ⟶ d') : CategoryStruct.comp (actionUnitIso d).hom f = CategoryStruct.comp (actionHomRight (tensorUnit C) f) (actionUnitIso d').hom
- whiskerLeft_actionHomLeft (c : C) {c' c'' : C} (f : c' ⟶ c'') (d : D) : actionHomLeft (whiskerLeft c f) d = CategoryStruct.comp (actionAssocIso c c' d).hom (CategoryStruct.comp (actionHomRight c (actionHomLeft f d)) (actionAssocIso c c'' d).inv)
- whiskerRight_actionHomLeft {c c' : C} (c'' : C) (f : c ⟶ c') (d : D) : actionHomLeft (whiskerRight f c'') d = CategoryStruct.comp (actionAssocIso c c'' d).hom (CategoryStruct.comp (actionHomLeft f (actionObj c'' d)) (actionAssocIso c' c'' d).inv)
- associator_actionHom (c₁ c₂ c₃ : C) (d : D) : CategoryStruct.comp (actionHomLeft (associator c₁ c₂ c₃).hom d) (CategoryStruct.comp (actionAssocIso c₁ (tensorObj c₂ c₃) d).hom (actionHomRight c₁ (actionAssocIso c₂ c₃ d).hom)) = CategoryStruct.comp (actionAssocIso (tensorObj c₁ c₂) c₃ d).hom (actionAssocIso c₁ c₂ (actionObj c₃ d)).hom
- leftUnitor_actionHom (c : C) (d : D) : actionHomLeft (leftUnitor c).hom d = CategoryStruct.comp (actionAssocIso (tensorUnit C) c d).hom (actionUnitIso (actionObj c d)).hom
- rightUnitor_actionHom (c : C) (d : D) : actionHomLeft (rightUnitor c).hom d = CategoryStruct.comp (actionAssocIso c (tensorUnit C) d).hom (actionHomRight c (actionUnitIso d).hom)
Instances
A monoidal category acts on itself through the tensor product.
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Bundle the action of C on D as a functor C ⥤ D ⥤ D.
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Bundle d ↦ c ⊙ₗ d as a functor.
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Bundle c ↦ c ⊙ₗ d as a functor.
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Bundle αₗ _ _ _ as an isomorphism of trifunctors.
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Bundle λₗ _ as an isomorphism of functors.
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