Chosen pullbacks #
Given two morphisms f₁ : X₁ ⟶ S and f₂ : X₂ ⟶ S, we introduce
a structure ChosenPullback f₁ f₂ which contains the data of
pullback of f₁ and f₂.
TODO #
- relate this to
ChosenPullbacksAlongwhich is defined inLocallyCartesianClosed.ChosenPullbacksAlong.
Given two morphisms f₁ : X₁ ⟶ S and f₂ : X₂ ⟶ S, this is the choice
of a pullback of f₁ and f₂.
- pullback : C
the pullback
the first projection
the second projection
- isLimit : IsLimit (PullbackCone.mk self.p₁ self.p₂ ⋯)
pullbackis a pullback off₁andf₂ the projection
pullback ⟶ S
Instances For
Given f₁ : X₁ ⟶ S, f₂ : X₂ ⟶ S, h : ChosenPullback f₁ f₂ and morphisms
g₁ : Y ⟶ X₁, g₂ : Y ⟶ X₂ and b : Y ⟶ S, this structure contains a morphism
Y ⟶ h.pullback such that f ≫ h.p₁ = g₁, f ≫ h.p₂ = g₂ and f ≫ h.p = b.
(This is nonempty only when g₁ ≫ f₁ = g₂ ≫ f₂ = b.)
a lifting to the pullback
Instances For
Given f : X ⟶ S and h : ChosenPullback f f, this is the type of
morphisms l : X ⟶ h.pullback that are equal to the diagonal map.
Equations
Instances For
Given three morphisms f₁ : X₁ ⟶ S, f₂ : X₂ ⟶ S and f₃ : X₃ ⟶ S, and chosen
pullbacks for (f₁, f₂), (f₂, f₃) and (f₁, f₃), this structure contains the data
of a wide pullback of the three morphisms f₁, f₂ and f₃.
- chosenPullback : ChosenPullback h₁₂.p₂ h₂₃.p₁
The projection from the wide pullback of
(f₁, f₂, f₃)toS.The projection from the wide pullback of
(f₁, f₂, f₃)toX₁.The projection from the wide pullback of
(f₁, f₂, f₃)toX₃.- l : h₁₃.LiftStruct self.p₁ self.p₃ self.p
A morphism from the wide pullback
(f₁, f₂, f₃)to the pullback off₁andf₃that is compatible with projections.
Instances For
The chosen wide pullback of (f₁, f₂, f₃).
Equations
Instances For
The projection from the wide pullback of (f₁, f₂, f₃) to the pullback of f₁ and f₃.
Instances For
The projection from the wide pullback of (f₁, f₂, f₃) to the pullback of f₁ and f₂.
Equations
- h.p₁₂ = h.chosenPullback.p₁
Instances For
The projection from the wide pullback of (f₁, f₂, f₃) to the pullback of f₂ and f₃.
Equations
- h.p₂₃ = h.chosenPullback.p₂
Instances For
The projection from the wide pullback of (f₁, f₂, f₃) to X₂.
Equations
- h.p₂ = h.chosenPullback.p