Right derived functors #
In this file, given a functor F : C ⥤ H
, and L : C ⥤ D
that is a
localization functor for W : MorphismProperty C
, we define
F.totalRightDerived L W : D ⥤ H
as the left Kan extension of F
along L
: it is defined if the type class F.HasRightDerivedFunctor W
asserting the existence of a left Kan extension is satisfied.
(The name totalRightDerived
is to avoid name-collision with
Functor.rightDerived
which are the right derived functors in
the context of abelian categories.)
Given RF : D ⥤ H
and α : F ⟶ L ⋙ RF
, we also introduce a type class
F.IsRightDerivedFunctor α W
saying that α
is a left Kan extension of F
along the localization functor L
.
TODO #
- refactor
Functor.rightDerived
(andFunctor.leftDerived
) when the necessary material enters mathlib: derived categories, injective/projective derivability structures, existence of derived functors from derivability structures.
References #
- https://ncatlab.org/nlab/show/derived+functor
A functor RF : D ⥤ H
is a right derived functor of F : C ⥤ H
if it is equipped with a natural transformation α : F ⟶ L ⋙ RF
which makes it a left Kan extension of F
along L
,
where L : C ⥤ D
is a localization functor for W : MorphismProperty C
.
- isLeftKanExtension' : RF.IsLeftKanExtension α
Instances
Constructor for natural transformations from a right derived functor.
Equations
- RF.rightDerivedDesc α W G β = RF.descOfIsLeftKanExtension α G β
Instances For
The natural transformation RF ⟶ RF'
on right derived functors that is
induced by a natural transformation F ⟶ F'
.
Equations
- RF.rightDerivedNatTrans RF' α α' W τ = RF.rightDerivedDesc α W RF' (CategoryTheory.CategoryStruct.comp τ α')
Instances For
The natural isomorphism RF ≅ RF'
on right derived functors that is
induced by a natural isomorphism F ≅ F'
.
Equations
- RF.rightDerivedNatIso RF' α α' W τ = { hom := RF.rightDerivedNatTrans RF' α α' W τ.hom, inv := RF'.rightDerivedNatTrans RF α' α W τ.inv, hom_inv_id := ⋯, inv_hom_id := ⋯ }
Instances For
Uniqueness (up to a natural isomorphism) of the right derived functor.
Equations
- RF.rightDerivedUnique RF' α α'₂ W = RF.rightDerivedNatIso RF' α α'₂ W (CategoryTheory.Iso.refl F)
Instances For
A functor F : C ⥤ H
has a right derived functor with respect to
W : MorphismProperty C
if it has a left Kan extension along
W.Q : C ⥤ W.Localization
(or any localization functor L : C ⥤ D
for W
, see hasRightDerivedFunctor_iff
).
- hasLeftKanExtension' : W.Q.HasLeftKanExtension F
Instances
Given a functor F : C ⥤ H
, and a localization functor L : D ⥤ H
for W
,
this is the right derived functor D ⥤ H
of F
, i.e. the left Kan extension
of F
along L
.
Equations
- CategoryTheory.Functor.totalRightDerived L W = L.leftKanExtension F
Instances For
The canonical natural transformation F ⟶ L ⋙ F.totalRightDerived L W
.
Equations
- CategoryTheory.Functor.totalRightDerivedUnit L W = L.leftKanExtensionUnit F