Cones and cocones #
We define Cone F, a cone over a functor F,
and F.cones : Cᵒᵖ ⥤ Type, the functor associating to X the cones over F with cone point X.
A cone c is defined by specifying its cone point c.pt and a natural transformation c.π
from the constant c.pt valued functor to F.
We provide c.w f : c.π.app j ≫ F.map f = c.π.app j' for any f : j ⟶ j'
as a wrapper for c.π.naturality f avoiding unneeded identity morphisms.
We define c.extend f, where c : cone F and f : Y ⟶ c.pt for some other Y,
which replaces the cone point by Y and inserts f into each of the components of the cone.
Similarly we have c.whisker F producing a Cone (E ⋙ F)
We define morphisms of cones, and the category of cones.
We define Cone.postcompose α : cone F ⥤ cone G for α a natural transformation F ⟶ G.
And, of course, we dualise all this to cocones as well.
For more results about the category of cones, see cone_category.lean.
If F : J ⥤ C then F.cones is the functor assigning to an object X : C the
type of natural transformations from the constant functor with value X to F.
An object representing this functor is a limit of F.
Equations
- CategoryTheory.Functor.cones F = CategoryTheory.Functor.comp (CategoryTheory.Functor.const J).op (CategoryTheory.yoneda.obj F)
Instances For
If F : J ⥤ C then F.cocones is the functor assigning to an object (X : C)
the type of natural transformations from F to the constant functor with value X.
An object corepresenting this functor is a colimit of F.
Equations
- CategoryTheory.Functor.cocones F = CategoryTheory.Functor.comp (CategoryTheory.Functor.const J) (CategoryTheory.coyoneda.obj (Opposite.op F))
Instances For
Functorially associated to each functor J ⥤ C, we have the C-presheaf consisting of
cones with a given cone point.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Contravariantly associated to each functor J ⥤ C, we have the C-copresheaf consisting of
cocones with a given cocone point.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A c : Cone F is:
Example: if J is a category coming from a poset then the data required to make
a term of type Cone F is morphisms πⱼ : c.pt ⟶ F j for all j : J and,
for all i ≤ j in J, morphisms πᵢⱼ : F i ⟶ F j such that πᵢ ≫ πᵢⱼ = πᵢ.
Cone F is equivalent, via cone.equiv below, to Σ X, F.cones.obj X.
- pt : C
An object of
C - π : (CategoryTheory.Functor.const J).obj self.pt ⟶ F
A natural transformation from the constant functor at
XtoF
Instances For
Equations
- One or more equations did not get rendered due to their size.
A c : Cocone F is
For example, if the source J of F is a partially ordered set, then to give
c : Cocone F is to give a collection of morphisms ιⱼ : F j ⟶ c.pt and, for
all j ≤ k in J, morphisms ιⱼₖ : F j ⟶ F k such that Fⱼₖ ≫ Fₖ = Fⱼ for all j ≤ k.
Cocone F is equivalent, via Cone.equiv below, to Σ X, F.cocones.obj X.
- pt : C
An object of
C - ι : F ⟶ (CategoryTheory.Functor.const J).obj self.pt
A natural transformation from
Fto the constant functor atpt
Instances For
Equations
- One or more equations did not get rendered due to their size.
The isomorphism between a cone on F and an element of the functor F.cones.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A map to the vertex of a cone naturally induces a cone by composition.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A map to the vertex of a cone induces a cone by composition.
Equations
- CategoryTheory.Limits.Cone.extend c f = { pt := X, π := (CategoryTheory.Limits.Cone.extensions c).app (Opposite.op X) { down := f } }
Instances For
Whisker a cone by precomposition of a functor.
Equations
- CategoryTheory.Limits.Cone.whisker E c = { pt := c.pt, π := CategoryTheory.whiskerLeft E c.π }
Instances For
The isomorphism between a cocone on F and an element of the functor F.cocones.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A map from the vertex of a cocone naturally induces a cocone by composition.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A map from the vertex of a cocone induces a cocone by composition.
Equations
- CategoryTheory.Limits.Cocone.extend c f = { pt := Y, ι := (CategoryTheory.Limits.Cocone.extensions c).app Y { down := f } }
Instances For
Whisker a cocone by precomposition of a functor. See whiskering for a functorial
version.
Equations
- CategoryTheory.Limits.Cocone.whisker E c = { pt := c.pt, ι := CategoryTheory.whiskerLeft E c.ι }
Instances For
A cone morphism between two cones for the same diagram is a morphism of the cone points which commutes with the cone legs.
- hom : A.pt ⟶ B.pt
A morphism between the two vertex objects of the cones
- w : ∀ (j : J), CategoryTheory.CategoryStruct.comp self.hom (B.π.app j) = A.π.app j
The triangle consisting of the two natural transformations and
homcommutes
Instances For
Equations
- CategoryTheory.Limits.inhabitedConeMorphism A = { default := { hom := CategoryTheory.CategoryStruct.id A.pt, w := ⋯ } }
The category of cones on a given diagram.
Equations
- CategoryTheory.Limits.Cone.category = CategoryTheory.Category.mk ⋯ ⋯ ⋯
To give an isomorphism between cones, it suffices to give an isomorphism between their vertices which commutes with the cone maps.
Equations
- CategoryTheory.Limits.Cones.ext φ w = { hom := { hom := φ.hom, w := ⋯ }, inv := { hom := φ.inv, w := ⋯ }, hom_inv_id := ⋯, inv_hom_id := ⋯ }
Instances For
Eta rule for cones.
Equations
Instances For
Given a cone morphism whose object part is an isomorphism, produce an isomorphism of cones.
Functorially postcompose a cone for F by a natural transformation F ⟶ G to give a cone for G.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Postcomposing a cone by the composite natural transformation α ≫ β is the same as
postcomposing by α and then by β.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Postcomposing by the identity does not change the cone up to isomorphism.
Equations
- One or more equations did not get rendered due to their size.
Instances For
If F and G are naturally isomorphic functors, then they have equivalent categories of
cones.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Whiskering on the left by E : K ⥤ J gives a functor from Cone F to Cone (E ⋙ F).
Equations
- One or more equations did not get rendered due to their size.
Instances For
Whiskering by an equivalence gives an equivalence between categories of cones.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The categories of cones over F and G are equivalent if F and G are naturally isomorphic
(possibly after changing the indexing category by an equivalence).
Equations
Instances For
Forget the cone structure and obtain just the cone point.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A functor G : C ⥤ D sends cones over F to cones over F ⋙ G functorially.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
- One or more equations did not get rendered due to their size.
Equations
- ⋯ = ⋯
If e : C ≌ D is an equivalence of categories, then functoriality F e.functor induces an
equivalence between cones over F and cones over F ⋙ e.functor.
Equations
- One or more equations did not get rendered due to their size.
Instances For
If F reflects isomorphisms, then Cones.functoriality F reflects isomorphisms
as well.
Equations
- ⋯ = ⋯
A cocone morphism between two cocones for the same diagram is a morphism of the cocone points which commutes with the cocone legs.
- hom : A.pt ⟶ B.pt
A morphism between the (co)vertex objects in
C - w : ∀ (j : J), CategoryTheory.CategoryStruct.comp (A.ι.app j) self.hom = B.ι.app j
The triangle made from the two natural transformations and
homcommutes
Instances For
Equations
- CategoryTheory.Limits.inhabitedCoconeMorphism A = { default := { hom := CategoryTheory.CategoryStruct.id A.pt, w := ⋯ } }
Equations
- CategoryTheory.Limits.Cocone.category = CategoryTheory.Category.mk ⋯ ⋯ ⋯
To give an isomorphism between cocones, it suffices to give an isomorphism between their vertices which commutes with the cocone maps.
Equations
- CategoryTheory.Limits.Cocones.ext φ w = { hom := { hom := φ.hom, w := ⋯ }, inv := { hom := φ.inv, w := ⋯ }, hom_inv_id := ⋯, inv_hom_id := ⋯ }
Instances For
Eta rule for cocones.
Equations
Instances For
Given a cocone morphism whose object part is an isomorphism, produce an isomorphism of cocones.
Functorially precompose a cocone for F by a natural transformation G ⟶ F to give a cocone
for G.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Precomposing a cocone by the composite natural transformation α ≫ β is the same as
precomposing by β and then by α.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Precomposing by the identity does not change the cocone up to isomorphism.
Equations
- One or more equations did not get rendered due to their size.
Instances For
If F and G are naturally isomorphic functors, then they have equivalent categories of
cocones.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Whiskering on the left by E : K ⥤ J gives a functor from Cocone F to Cocone (E ⋙ F).
Equations
- One or more equations did not get rendered due to their size.
Instances For
Whiskering by an equivalence gives an equivalence between categories of cones.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The categories of cocones over F and G are equivalent if F and G are naturally isomorphic
(possibly after changing the indexing category by an equivalence).
Equations
Instances For
Forget the cocone structure and obtain just the cocone point.
Equations
- One or more equations did not get rendered due to their size.
Instances For
A functor G : C ⥤ D sends cocones over F to cocones over F ⋙ G functorially.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
- One or more equations did not get rendered due to their size.
Equations
- ⋯ = ⋯
If e : C ≌ D is an equivalence of categories, then functoriality F e.functor induces an
equivalence between cocones over F and cocones over F ⋙ e.functor.
Equations
- One or more equations did not get rendered due to their size.
Instances For
If F reflects isomorphisms, then Cocones.functoriality F reflects isomorphisms
as well.
Equations
- ⋯ = ⋯
The image of a cone in C under a functor G : C ⥤ D is a cone in D.
Equations
- H.mapCone c = (CategoryTheory.Limits.Cones.functoriality F H).obj c
Instances For
The image of a cocone in C under a functor G : C ⥤ D is a cocone in D.
Equations
- H.mapCocone c = (CategoryTheory.Limits.Cocones.functoriality F H).obj c
Instances For
Given a cone morphism c ⟶ c', construct a cone morphism on the mapped cones functorially.
Equations
Instances For
Given a cocone morphism c ⟶ c', construct a cocone morphism on the mapped cocones
functorially.
Equations
Instances For
If H is an equivalence, we invert H.mapCone and get a cone for F from a cone
for F ⋙ H.
Equations
Instances For
mapCone is the left inverse to mapConeInv.
Equations
Instances For
MapCone is the right inverse to mapConeInv.
Equations
- CategoryTheory.Functor.mapConeInvMapCone H c = (CategoryTheory.Limits.Cones.functorialityEquivalence F (CategoryTheory.Functor.asEquivalence H)).unitIso.symm.app c
Instances For
If H is an equivalence, we invert H.mapCone and get a cone for F from a cone
for F ⋙ H.
Equations
Instances For
mapCocone is the left inverse to mapCoconeInv.
Equations
Instances For
mapCocone is the right inverse to mapCoconeInv.
Equations
- CategoryTheory.Functor.mapCoconeInvMapCocone H c = (CategoryTheory.Limits.Cocones.functorialityEquivalence F (CategoryTheory.Functor.asEquivalence H)).unitIso.symm.app c
Instances For
functoriality F _ ⋙ postcompose (whisker_left F _) simplifies to functoriality F _.
Equations
- CategoryTheory.Functor.functorialityCompPostcompose α = CategoryTheory.NatIso.ofComponents (fun (c : CategoryTheory.Limits.Cone F) => CategoryTheory.Limits.Cones.ext (α.app c.pt) ⋯) ⋯
Instances For
For F : J ⥤ C, given a cone c : Cone F, and a natural isomorphism α : H ≅ H' for functors
H H' : C ⥤ D, the postcomposition of the cone H.mapCone using the isomorphism α is
isomorphic to the cone H'.mapCone.
Equations
Instances For
mapCone commutes with postcompose. In particular, for F : J ⥤ C, given a cone c : Cone F, a
natural transformation α : F ⟶ G and a functor H : C ⥤ D, we have two obvious ways of producing
a cone over G ⋙ H, and they are both isomorphic.
Equations
- CategoryTheory.Functor.mapConePostcompose H = CategoryTheory.Limits.Cones.ext (CategoryTheory.Iso.refl (H.mapCone ((CategoryTheory.Limits.Cones.postcompose α).obj c)).pt) ⋯
Instances For
mapCone commutes with postcomposeEquivalence
Equations
- One or more equations did not get rendered due to their size.
Instances For
functoriality F _ ⋙ precompose (whiskerLeft F _) simplifies to functoriality F _.
Equations
- CategoryTheory.Functor.functorialityCompPrecompose α = CategoryTheory.NatIso.ofComponents (fun (c : CategoryTheory.Limits.Cocone F) => CategoryTheory.Limits.Cocones.ext (α.app c.pt) ⋯) ⋯
Instances For
For F : J ⥤ C, given a cocone c : Cocone F, and a natural isomorphism α : H ≅ H' for functors
H H' : C ⥤ D, the precomposition of the cocone H.mapCocone using the isomorphism α is
isomorphic to the cocone H'.mapCocone.
Equations
Instances For
map_cocone commutes with precompose. In particular, for F : J ⥤ C, given a cocone
c : Cocone F, a natural transformation α : F ⟶ G and a functor H : C ⥤ D, we have two obvious
ways of producing a cocone over G ⋙ H, and they are both isomorphic.
Equations
- CategoryTheory.Functor.mapCoconePrecompose H = CategoryTheory.Limits.Cocones.ext (CategoryTheory.Iso.refl (H.mapCocone ((CategoryTheory.Limits.Cocones.precompose α).obj c)).pt) ⋯
Instances For
mapCocone commutes with precomposeEquivalence
Equations
- One or more equations did not get rendered due to their size.
Instances For
Equations
Instances For
mapCocone commutes with whisker
Equations
- CategoryTheory.Functor.mapCoconeWhisker H = CategoryTheory.Limits.Cocones.ext (CategoryTheory.Iso.refl (H.mapCocone (CategoryTheory.Limits.Cocone.whisker E c)).pt) ⋯
Instances For
Change a Cocone F into a Cone F.op.
Equations
- CategoryTheory.Limits.Cocone.op c = { pt := Opposite.op c.pt, π := CategoryTheory.NatTrans.op c.ι }
Instances For
Change a Cone F into a Cocone F.op.
Equations
- CategoryTheory.Limits.Cone.op c = { pt := Opposite.op c.pt, ι := CategoryTheory.NatTrans.op c.π }
Instances For
Change a Cocone F.op into a Cone F.
Equations
- CategoryTheory.Limits.Cocone.unop c = { pt := c.pt.unop, π := CategoryTheory.NatTrans.removeOp c.ι }
Instances For
Change a Cone F.op into a Cocone F.
Equations
- CategoryTheory.Limits.Cone.unop c = { pt := c.pt.unop, ι := CategoryTheory.NatTrans.removeOp c.π }
Instances For
The category of cocones on F
is equivalent to the opposite category of
the category of cones on the opposite of F.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Change a cocone on F.leftOp : Jᵒᵖ ⥤ C to a cocone on F : J ⥤ Cᵒᵖ.
Equations
- CategoryTheory.Limits.coneOfCoconeLeftOp c = { pt := Opposite.op c.pt, π := CategoryTheory.NatTrans.removeLeftOp c.ι }
Instances For
Change a cone on F : J ⥤ Cᵒᵖ to a cocone on F.leftOp : Jᵒᵖ ⥤ C.
Equations
- CategoryTheory.Limits.coconeLeftOpOfCone c = { pt := c.pt.unop, ι := CategoryTheory.NatTrans.leftOp c.π }
Instances For
Change a cone on F.leftOp : Jᵒᵖ ⥤ C to a cocone on F : J ⥤ Cᵒᵖ.
Equations
- CategoryTheory.Limits.coconeOfConeLeftOp c = { pt := Opposite.op c.pt, ι := CategoryTheory.NatTrans.removeLeftOp c.π }
Instances For
Change a cocone on F : J ⥤ Cᵒᵖ to a cone on F.leftOp : Jᵒᵖ ⥤ C.
Equations
- CategoryTheory.Limits.coneLeftOpOfCocone c = { pt := c.pt.unop, π := CategoryTheory.NatTrans.leftOp c.ι }
Instances For
Change a cocone on F.rightOp : J ⥤ Cᵒᵖ to a cone on F : Jᵒᵖ ⥤ C.
Equations
- CategoryTheory.Limits.coneOfCoconeRightOp c = { pt := c.pt.unop, π := CategoryTheory.NatTrans.removeRightOp c.ι }
Instances For
Change a cone on F : Jᵒᵖ ⥤ C to a cocone on F.rightOp : Jᵒᵖ ⥤ C.
Equations
- CategoryTheory.Limits.coconeRightOpOfCone c = { pt := Opposite.op c.pt, ι := CategoryTheory.NatTrans.rightOp c.π }
Instances For
Change a cone on F.rightOp : J ⥤ Cᵒᵖ to a cocone on F : Jᵒᵖ ⥤ C.
Equations
- CategoryTheory.Limits.coconeOfConeRightOp c = { pt := c.pt.unop, ι := CategoryTheory.NatTrans.removeRightOp c.π }
Instances For
Change a cocone on F : Jᵒᵖ ⥤ C to a cone on F.rightOp : J ⥤ Cᵒᵖ.
Equations
- CategoryTheory.Limits.coneRightOpOfCocone c = { pt := Opposite.op c.pt, π := CategoryTheory.NatTrans.rightOp c.ι }
Instances For
Change a cocone on F.unop : J ⥤ C into a cone on F : Jᵒᵖ ⥤ Cᵒᵖ.
Equations
- CategoryTheory.Limits.coneOfCoconeUnop c = { pt := Opposite.op c.pt, π := CategoryTheory.NatTrans.removeUnop c.ι }
Instances For
Change a cone on F : Jᵒᵖ ⥤ Cᵒᵖ into a cocone on F.unop : J ⥤ C.
Equations
- CategoryTheory.Limits.coconeUnopOfCone c = { pt := c.pt.unop, ι := CategoryTheory.NatTrans.unop c.π }
Instances For
Change a cone on F.unop : J ⥤ C into a cocone on F : Jᵒᵖ ⥤ Cᵒᵖ.
Equations
- CategoryTheory.Limits.coconeOfConeUnop c = { pt := Opposite.op c.pt, ι := CategoryTheory.NatTrans.removeUnop c.π }
Instances For
Change a cocone on F : Jᵒᵖ ⥤ Cᵒᵖ into a cone on F.unop : J ⥤ C.
Equations
- CategoryTheory.Limits.coneUnopOfCocone c = { pt := c.pt.unop, π := CategoryTheory.NatTrans.unop c.ι }
Instances For
The opposite cocone of the image of a cone is the image of the opposite cocone.
Equations
- CategoryTheory.Functor.mapConeOp G t = CategoryTheory.Limits.Cocones.ext (CategoryTheory.Iso.refl (CategoryTheory.Limits.Cone.op (G.mapCone t)).pt) ⋯
Instances For
The opposite cone of the image of a cocone is the image of the opposite cone.
Equations
- CategoryTheory.Functor.mapCoconeOp G = CategoryTheory.Limits.Cones.ext (CategoryTheory.Iso.refl (CategoryTheory.Limits.Cocone.op (G.mapCocone t)).pt) ⋯