Triangles #
This file contains the definition of triangles in an additive category with an additive shift. It also defines morphisms between these triangles.
TODO: generalise this to n-angles in n-angulated categories as in https://arxiv.org/abs/1006.4592
A triangle in C is a sextuple (X,Y,Z,f,g,h) where X,Y,Z are objects of C,
and f : X ⟶ Y, g : Y ⟶ Z, h : Z ⟶ X⟦1⟧ are morphisms in C.
- mk' :: (
- obj₁ : C
the first object of a triangle
- obj₂ : C
the second object of a triangle
- obj₃ : C
the third object of a triangle
the first morphism of a triangle
the second morphism of a triangle
the third morphism of a triangle
- )
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A triangle (X,Y,Z,f,g,h) in C is defined by the morphisms f : X ⟶ Y, g : Y ⟶ Z
and h : Z ⟶ X⟦1⟧.
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For each object in C, there is a triangle of the form (X,X,0,𝟙 X,0,0)
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A morphism of triangles (X,Y,Z,f,g,h) ⟶ (X',Y',Z',f',g',h') in C is a triple of morphisms
a : X ⟶ X', b : Y ⟶ Y', c : Z ⟶ Z' such that
a ≫ f' = f ≫ b, b ≫ g' = g ≫ c, and a⟦1⟧' ≫ h = h' ≫ c.
In other words, we have a commutative diagram:
f g h
X ───> Y ───> Z ───> X⟦1⟧
│ │ │ │
│a │b │c │a⟦1⟧'
V V V V
X' ───> Y' ───> Z' ───> X'⟦1⟧
f' g' h'
the first morphism in a triangle morphism
the second morphism in a triangle morphism
the third morphism in a triangle morphism
- comm₁ : CategoryStruct.comp T₁.mor₁ self.hom₂ = CategoryStruct.comp self.hom₁ T₂.mor₁
the first commutative square of a triangle morphism
- comm₂ : CategoryStruct.comp T₁.mor₂ self.hom₃ = CategoryStruct.comp self.hom₂ T₂.mor₂
the second commutative square of a triangle morphism
- comm₃ : CategoryStruct.comp T₁.mor₃ ((shiftFunctor C 1).map self.hom₁) = CategoryStruct.comp self.hom₃ T₂.mor₃
the third commutative square of a triangle morphism
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the second commutative square of a triangle morphism
the third commutative square of a triangle morphism
the first commutative square of a triangle morphism
The identity triangle morphism.
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Composition of triangle morphisms gives a triangle morphism.
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Triangles with triangle morphisms form a category.
Make a morphism between triangles from the required data.
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Make an isomorphism between triangles from the required data.
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The obvious triangle X₁ ⟶ X₁ ⊞ X₂ ⟶ X₂ ⟶ X₁⟦1⟧.
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The obvious triangle X₁ ⟶ X₁ ⨯ X₂ ⟶ X₂ ⟶ X₁⟦1⟧.
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The canonical isomorphism of triangles
binaryProductTriangle X₁ X₂ ≅ binaryBiproductTriangle X₁ X₂.
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The product of a family of triangles.
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A projection from the product of a family of triangles.
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The fan given by productTriangle T.
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A family of morphisms T' ⟶ T j lifts to a morphism T' ⟶ productTriangle T.
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The triangle productTriangle T satisfies the universal property of the categorical
product of the triangles T.
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The functor C ⥤ Triangle C which sends X to contractibleTriangle X.
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The first projection Triangle C ⥤ C.
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The second projection Triangle C ⥤ C.
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The third projection Triangle C ⥤ C.
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The first morphism of a triangle, as a natural transformation π₁ ⟶ π₂.
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The second morphism of a triangle, as a natural transformation π₂ ⟶ π₃.
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The third morphism of a triangle, as a natural
transformation π₃ ⟶ π₁ ⋙ shiftFunctor _ (1 : ℤ).
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Constructor for functors to the category of triangles.
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Constructor for natural transformations between functors to the category of triangles.
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Constructor for natural transformations between functors constructed
with functorMk.
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Constructor for natural isomorphisms between functors to the category of triangles.
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Constructor for natural isomorphisms between functors constructed
with functorMk.