The pretriangulated structure on the homotopy category of complexes
In this file, we define the pretriangulated structure on the homotopy
category HomotopyCategory C (ComplexShape.up ℤ)
of an additive category C
.
The distinguished triangles are the triangles that are isomorphic to the
image in the homotopy category of the standard triangle
K ⟶ L ⟶ mappingCone φ ⟶ K⟦(1 : ℤ)⟧
for some morphism of
cochain complexes φ : K ⟶ L
.
This result first appeared in the Liquid Tensor Experiment. In the LTE, the formalization followed the Stacks Project: in particular, the distinguished triangles were defined using degreewise-split short exact sequences of cochain complexes. Here, we follow the original definitions in [Verdiers's thesis, I.3][verdier1996] (with the better sign conventions from the introduction of [Brian Conrad's book Grothendieck duality and base change][conrad2000]).
References #
- [Jean-Louis Verdier, Des catégories dérivées des catégories abéliennes][verdier1996]
- [Brian Conrad, Grothendieck duality and base change][conrad2000]
- https://stacks.math.columbia.edu/tag/014P
The standard triangle K ⟶ L ⟶ mappingCone φ ⟶ K⟦(1 : ℤ)⟧
in CochainComplex C ℤ
attached to a morphism φ : K ⟶ L
. It involves φ
, inr φ : L ⟶ mappingCone φ
and
the morphism induced by the 1
-cocycle -mappingCone.fst φ
.
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Instances For
The (distinguished) triangle in the homotopy category that is associated to
a morphism φ : K ⟶ L
in the category CochainComplex C ℤ
.
Equations
- CochainComplex.mappingCone.triangleh φ = (HomotopyCategory.quotient C (ComplexShape.up ℤ)).mapTriangle.obj (CochainComplex.mappingCone.triangle φ)
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The mapping cone of the identity is contractible.
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The morphism mappingCone φ₁ ⟶ mappingCone φ₂
that is induced by a square that
is commutative up to homotopy.
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The morphism triangleh φ₁ ⟶ triangleh φ₂
that is induced by a square that
is commutative up to homotopy.
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The morphism mappingCone φ₁ ⟶ mappingCone φ₂
that is induced by a commutative square.
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The morphism triangle φ₁ ⟶ triangle φ₂
that is induced by a commutative square.
Equations
- CochainComplex.mappingCone.triangleMap φ₁ φ₂ a b comm = { hom₁ := a, hom₂ := b, hom₃ := CochainComplex.mappingCone.map φ₁ φ₂ a b comm, comm₁ := comm, comm₂ := ⋯, comm₃ := ⋯ }
Instances For
Given φ : K ⟶ L
, K⟦(1 : ℤ)⟧
is homotopy equivalent to
the mapping cone of inr φ : L ⟶ mappingCone φ
.
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Auxiliary definition for rotateTrianglehIso
.
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The canonical isomorphism of triangles (triangleh φ).rotate ≅ (triangleh (inr φ))
.
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The canonical isomorphism (mappingCone φ)⟦n⟧ ≅ mappingCone (φ⟦n⟧')
.
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The canonical isomorphism (triangle φ)⟦n⟧ ≅ triangle (φ⟦n⟧')
.
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The canonical isomorphism (triangleh φ)⟦n⟧ ≅ triangleh (φ⟦n⟧')
.
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If φ : K ⟶ L
is a morphism of cochain complexes in C
and G : C ⥤ D
is an
additive functor, then the image by G
of the triangle triangle φ
identifies to
the triangle associated to the image of φ
by G
.
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If φ : K ⟶ L
is a morphism of cochain complexes in C
and G : C ⥤ D
is an
additive functor, then the image by G
of the triangle triangleh φ
identifies to
the triangle associated to the image of φ
by G
.
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A triangle in HomotopyCategory C (ComplexShape.up ℤ)
is distinguished if it is isomorphic to
the triangle CochainComplex.mappingCone.triangleh φ
for some morphism of cochain
complexes φ
.
Equations
- HomotopyCategory.Pretriangulated.distinguishedTriangles C T = ∃ (X : CochainComplex C ℤ) (Y : CochainComplex C ℤ) (φ : X ⟶ Y), Nonempty (T ≅ CochainComplex.mappingCone.triangleh φ)
Instances For
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Equations
- ⋯ = ⋯