Additive Functors #
A functor between two preadditive categories is called additive provided that the induced map on hom types is a morphism of abelian groups.
An additive functor between preadditive categories creates and preserves biproducts.
Conversely, if F : C ⥤ D
is a functor between preadditive categories, where C
has binary
biproducts, and if F
preserves binary biproducts, then F
is additive.
We also define the category of bundled additive functors.
Implementation details #
Functor.Additive
is a Prop
-valued class, defined by saying that for every two objects X
and
Y
, the map F.map : (X ⟶ Y) → (F.obj X ⟶ F.obj Y)
is a morphism of abelian groups.
A functor F
is additive provided F.map
is an additive homomorphism.
the addition of two morphisms is mapped to the sum of their images
Instances
F.mapAddHom
is an additive homomorphism whose underlying function is F.map
.
Equations
- F.mapAddHom = AddMonoidHom.mk' (fun (f : X ⟶ Y) => F.map f) ⋯
Instances For
Bundled additive functors.
Equations
- (C ⥤+ D) = CategoryTheory.FullSubcategory fun (F : CategoryTheory.Functor C D) => F.Additive
Instances For
Equations
- CategoryTheory.instCategoryAdditiveFunctor C D = CategoryTheory.FullSubcategory.category fun (F : CategoryTheory.Functor C D) => F.Additive
the category of additive functors is denoted C ⥤+ D
Equations
- CategoryTheory.«term_⥤+_» = Lean.ParserDescr.trailingNode `CategoryTheory.«term_⥤+_» 26 27 (Lean.ParserDescr.binary `andthen (Lean.ParserDescr.symbol " ⥤+ ") (Lean.ParserDescr.cat `term 26))
Instances For
Equations
- CategoryTheory.instPreadditiveAdditiveFunctor C D = CategoryTheory.Preadditive.inducedCategory CategoryTheory.FullSubcategory.obj
An additive functor is in particular a functor.
Equations
- CategoryTheory.AdditiveFunctor.forget C D = CategoryTheory.fullSubcategoryInclusion fun (F : CategoryTheory.Functor C D) => F.Additive
Instances For
Turn an additive functor into an object of the category AdditiveFunctor C D
.
Equations
- CategoryTheory.AdditiveFunctor.of F = { obj := F, property := ⋯ }
Instances For
Turn a left exact functor into an additive functor.
Instances For
Turn a right exact functor into an additive functor.
Instances For
Turn an exact functor into an additive functor.