Whiskering #
Given a functor F : C ⥤ D
and functors G H : D ⥤ E
and a natural transformation α : G ⟶ H
,
we can construct a new natural transformation F ⋙ G ⟶ F ⋙ H
,
called whiskerLeft F α
. This is the same as the horizontal composition of 𝟙 F
with α
.
This operation is functorial in F
, and we package this as whiskeringLeft
. Here
(whiskeringLeft.obj F).obj G
is F ⋙ G
, and
(whiskeringLeft.obj F).map α
is whiskerLeft F α
.
(That is, we might have alternatively named this as the "left composition functor".)
We also provide analogues for composition on the right, and for these operations on isomorphisms.
We show the associators an unitor natural isomorphisms satisfy the triangle and pentagon identities.
If α : G ⟶ H
then
whiskerLeft F α : (F ⋙ G) ⟶ (F ⋙ H)
has components α.app (F.obj X)
.
Equations
- CategoryTheory.whiskerLeft F α = { app := fun (X : C) => α.app (F.obj X), naturality := ⋯ }
If α : G ⟶ H
then
whiskerRight α F : (G ⋙ F) ⟶ (G ⋙ F)
has components F.map (α.app X)
.
Equations
- CategoryTheory.whiskerRight α F = { app := fun (X : C) => F.map (α.app X), naturality := ⋯ }
Instances For
- CategoryTheory.Adjunction.whiskerRight_counit_iso_of_L_fully_faithful
- CategoryTheory.Adjunction.whiskerRight_unit_iso_of_R_fully_faithful
- CategoryTheory.Presheaf.instIsLocallySurjectiveHomObjForgetTypeWhiskerRightOpposite
- CategoryTheory.Presheaf.isLocallyInjective_forget
- CategoryTheory.instEpiFunctorWhiskerRightOfPreservesEpimorphisms
- CategoryTheory.instMonoFunctorWhiskerRightOfPreservesMonomorphisms
- CategoryTheory.isIso_whiskerRight
Left-composition gives a functor (C ⥤ D) ⥤ ((D ⥤ E) ⥤ (C ⥤ E))
.
(whiskeringLeft.obj F).obj G
is F ⋙ G
, and
(whiskeringLeft.obj F).map α
is whiskerLeft F α
.
Equations
- One or more equations did not get rendered due to their size.
Right-composition gives a functor (D ⥤ E) ⥤ ((C ⥤ D) ⥤ (C ⥤ E))
.
(whiskeringRight.obj H).obj F
is F ⋙ H
, and
(whiskeringRight.obj H).map α
is whiskerRight α H
.
Equations
- One or more equations did not get rendered due to their size.
If F : D ⥤ E
is fully faithful, then so is
(whiskeringRight C D E).obj F : (C ⥤ D) ⥤ C ⥤ E
.
Equations
- One or more equations did not get rendered due to their size.
The isomorphism between left-whiskering on the identity functor and the identity of the functor between the resulting functor categories.
The isomorphism between left-whiskering on the composition of functors and the composition of two left-whiskering applications.
Equations
- CategoryTheory.whiskeringLeftObjCompIso F G = CategoryTheory.Iso.refl ((CategoryTheory.whiskeringLeft C D' E).obj (F.comp G))
The isomorphism between right-whiskering on the identity functor and the identity of the functor between the resulting functor categories.
Alias of CategoryTheory.whiskeringRightObjIdIso
.
The isomorphism between right-whiskering on the identity functor and the identity of the functor between the resulting functor categories.
The isomorphism between right-whiskering on the composition of functors and the composition of two right-whiskering applications.
Equations
- CategoryTheory.whiskeringRightObjCompIso F G = CategoryTheory.Iso.refl (((CategoryTheory.whiskeringRight E C D).obj F).comp ((CategoryTheory.whiskeringRight E D D').obj G))
If α : G ≅ H
is a natural isomorphism then
isoWhiskerLeft F α : (F ⋙ G) ≅ (F ⋙ H)
has components α.app (F.obj X)
.
Equations
- CategoryTheory.isoWhiskerLeft F α = ((CategoryTheory.whiskeringLeft C D E).obj F).mapIso α
If α : G ≅ H
then
isoWhiskerRight α F : (G ⋙ F) ≅ (H ⋙ F)
has components F.map_iso (α.app X)
.
Equations
- CategoryTheory.isoWhiskerRight α F = ((CategoryTheory.whiskeringRight C D E).obj F).mapIso α
The obvious functor (C₁ ⥤ D₁) ⥤ (C₂ ⥤ D₂) ⥤ (D₁ ⥤ D₂ ⥤ E) ⥤ (C₁ ⥤ C₂ ⥤ E)
.
Equations
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Auxiliary definition for whiskeringLeft₃
.
Equations
- One or more equations did not get rendered due to their size.
Auxiliary definition for whiskeringLeft₃
.
Equations
- One or more equations did not get rendered due to their size.
Auxiliary definition for whiskeringLeft₃
.
Equations
- One or more equations did not get rendered due to their size.
Auxiliary definition for whiskeringLeft₃
.
Equations
- One or more equations did not get rendered due to their size.
Auxiliary definition for whiskeringLeft₃
.
Equations
- One or more equations did not get rendered due to their size.
Auxiliary definition for whiskeringLeft₃
.
Equations
- One or more equations did not get rendered due to their size.
The obvious functor
(C₁ ⥤ D₁) ⥤ (C₂ ⥤ D₂) ⥤ (C₃ ⥤ D₃) ⥤ (D₁ ⥤ D₂ ⥤ D₃ ⥤ E) ⥤ (C₁ ⥤ C₂ ⥤ C₃ ⥤ E)
.
Equations
- One or more equations did not get rendered due to their size.
The "postcomposition" with a functor E ⥤ E'
gives a functor
(E ⥤ E') ⥤ (C₁ ⥤ C₂ ⥤ E) ⥤ C₁ ⥤ C₂ ⥤ E'
.
Equations
- CategoryTheory.Functor.postcompose₂ = (CategoryTheory.whiskeringRight C₂ E E').comp (CategoryTheory.whiskeringRight C₁ (CategoryTheory.Functor C₂ E) (CategoryTheory.Functor C₂ E'))
The "postcomposition" with a functor E ⥤ E'
gives a functor
(E ⥤ E') ⥤ (C₁ ⥤ C₂ ⥤ C₃ ⥤ E) ⥤ C₁ ⥤ C₂ ⥤ C₃ ⥤ E'
.
Equations
- One or more equations did not get rendered due to their size.