Action V G
, the category of actions of a monoid G
inside some category V
. #
The prototypical example is V = ModuleCat R
,
where Action (ModuleCat R) G
is the category of R
-linear representations of G
.
We check Action V G ≌ (CategoryTheory.singleObj G ⥤ V)
,
and construct the restriction functors res {G H : MonCat} (f : G ⟶ H) : Action V H ⥤ Action V G
.
When a group acts, we can lift the action to the group of automorphisms.
Equations
Instances For
Equations
- Action.inhabited' G = { default := { V := PUnit.{?u.10 + 1}, ρ := 1 } }
The trivial representation of a group.
Equations
- Action.trivial G = { V := AddCommGrp.of PUnit.{?u.10 + 1}, ρ := 1 }
Instances For
Equations
- Action.instInhabitedAddCommGrp G = { default := Action.trivial G }
A homomorphism of Action V G
s is a morphism between the underlying objects,
commuting with the action of G
.
- hom : M.V ⟶ N.V
- comm (g : ↑G) : CategoryTheory.CategoryStruct.comp (M.ρ g) self.hom = CategoryTheory.CategoryStruct.comp self.hom (N.ρ g)
Instances For
The identity morphism on an Action V G
.
Equations
- Action.Hom.id M = { hom := CategoryTheory.CategoryStruct.id M.V, comm := ⋯ }
Instances For
Equations
- Action.Hom.instInhabited M = { default := Action.Hom.id M }
The composition of two Action V G
homomorphisms is the composition of the underlying maps.
Equations
- p.comp q = { hom := CategoryTheory.CategoryStruct.comp p.hom q.hom, comm := ⋯ }
Instances For
Equations
- Action.instCategory = CategoryTheory.Category.mk ⋯ ⋯ ⋯
Construct an isomorphism of G
actions/representations
from an isomorphism of the underlying objects,
where the forward direction commutes with the group action.
Equations
- Action.mkIso f comm = { hom := { hom := f.hom, comm := comm }, inv := { hom := f.inv, comm := ⋯ }, hom_inv_id := ⋯, inv_hom_id := ⋯ }
Instances For
Auxiliary definition for functorCategoryEquivalence
.
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Instances For
Auxiliary definition for functorCategoryEquivalence
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Auxiliary definition for functorCategoryEquivalence
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Auxiliary definition for functorCategoryEquivalence
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The category of actions of G
in the category V
is equivalent to the functor category singleObj G ⥤ V
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
(implementation) The forgetful functor from bundled actions to the underlying objects.
Use the CategoryTheory.forget
API provided by the ConcreteCategory
instance below,
rather than using this directly.
Equations
- Action.forget V G = { obj := fun (M : Action V G) => M.V, map := fun {X Y : Action V G} (f : X ⟶ Y) => f.hom, map_id := ⋯, map_comp := ⋯ }
Instances For
Equations
- Action.instConcreteCategory V G = CategoryTheory.ConcreteCategory.mk ((Action.forget V G).comp CategoryTheory.ConcreteCategory.forget)
Equations
- Action.hasForgetToV V G = { forget₂ := Action.forget V G, forget_comp := ⋯ }
The forgetful functor is intertwined by functorCategoryEquivalence
with
evaluation at PUnit.star
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Actions/representations of the trivial group are just objects in the ambient category.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The "restriction" functor along a monoid homomorphism f : G ⟶ H
,
taking actions of H
to actions of G
.
(This makes sense for any homomorphism, but the name is natural when f
is a monomorphism.)
Equations
- One or more equations did not get rendered due to their size.
Instances For
The natural isomorphism from restriction along the identity homomorphism to
the identity functor on Action V G
.
Equations
- Action.resId V = CategoryTheory.NatIso.ofComponents (fun (M : Action V G) => Action.mkIso (CategoryTheory.Iso.refl ((Action.res V (CategoryTheory.CategoryStruct.id G)).obj M).V) ⋯) ⋯
Instances For
The natural isomorphism from the composition of restrictions along homomorphisms to the restriction along the composition of homomorphism.
Equations
- Action.resComp V f g = CategoryTheory.NatIso.ofComponents (fun (M : Action V K) => Action.mkIso (CategoryTheory.Iso.refl (((Action.res V g).comp (Action.res V f)).obj M).V) ⋯) ⋯
Instances For
A functor between categories induces a functor between
the categories of G
-actions within those categories.
Equations
- One or more equations did not get rendered due to their size.