Truncations for a t-structure #
Let t be a t-structure on a triangulated category C.
In this file, we extend the definition of the truncation functors
truncLT and truncGE for indices in ℤ to EInt,
as t.eTruncLT : EInt ⥤ C ⥤ C and t.eTruncGE : EInt ⥤ C ⥤ C.
The functor EInt ⥤ C ⥤ C which sends ⊥ to the zero functor,
n : ℤ to t.truncLT n and ⊤ to 𝟭 C.
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The functor EInt ⥤ C ⥤ C which sends ⊥ to 𝟭 C,
n : ℤ to t.truncGE n and ⊤ to the zero functor.
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The connecting homomorphism from t.eTruncGE to the
shift by 1 of t.eTruncLT.
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- t.eTruncGEδLT = { app := fun (a : WithBotTop ℤ) => WithBotTop.rec 0 t.truncGEδLT 0 a, naturality := ⋯ }
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The natural transformation t.eTruncLT.obj i ⟶ 𝟭 C for all i : EInt.
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- t.eTruncLTι i = t.eTruncLT.map (CategoryTheory.homOfLE ⋯)
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The natural transformation 𝟭 C ⟶ t.eTruncGE.obj i for all i : EInt.
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- t.eTruncGEπ i = t.eTruncGE.map (CategoryTheory.homOfLE ⋯)
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The (distinguished) triangles given by the natural transformations
t.eTruncLT.obj i ⟶ 𝟭 C ⟶ t.eTruncGE.obj i ⟶ ... for all i : EInt.
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The natural transformation t.eTruncGE.obj b ⟶ t.eTruncGE.obj a ⋙ t.eTruncGE.obj b
for all a and b in EInt.
Equations
- t.eTruncGEToGEGE a b = CategoryTheory.CategoryStruct.comp (t.eTruncGE.obj b).leftUnitor.inv (CategoryTheory.Functor.whiskerRight (t.eTruncGEπ a) (t.eTruncGE.obj b))
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The natural isomorphism t.eTruncGE.obj b ≅ t.eTruncGE.obj a ⋙ t.eTruncGE.obj b
when a and b in EInt satisfy a ≤ b.
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- t.eTruncGEIsoGEGE a b hab = CategoryTheory.asIso (t.eTruncGEToGEGE a b)
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The natural transformation t.eTruncLT.obj a ⋙ t.eTruncLT.obj b ⟶ t.eTruncLT.obj b
for all a and b in EInt.
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- t.eTruncLTLTToLT a b = CategoryTheory.CategoryStruct.comp (CategoryTheory.Functor.whiskerRight (t.eTruncLTι a) (t.eTruncLT.obj b)) (t.eTruncLT.obj b).leftUnitor.hom
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The natural isomorphism t.eTruncLT.obj a ⋙ t.eTruncLT.obj b ⟶ t.eTruncLT.obj b
when a and b in EInt satisfy b ≤ a.
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- t.eTruncLTLTIsoLT a b hab = CategoryTheory.asIso (t.eTruncLTLTToLT a b)
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The natural transformation from
t.eTruncLT.obj b ⋙ t.eTruncGE.obj a ⋙ t.eTruncLT.obj b to
t.eTruncGE.obj a ⋙ t.eTruncLT.obj b. (This is an isomorphism.)
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The natural transformation from
t.eTruncLT.obj b ⋙ t.eTruncGE.obj a ⋙ t.eTruncLT.obj b to
t.eTruncLT.obj b ⋙ t.eTruncGE.obj a. (This is an isomorphism.)
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The commutation natural isomorphism
t.eTruncGE.obj a ⋙ t.eTruncLT.obj b ≅ t.eTruncLT.obj b ⋙ t.eTruncGE.obj a
for all a and b in EInt.
Equations
- t.eTruncLTGEIsoGELT a b = (CategoryTheory.asIso (t.eTruncLTGELTSelfToLTGE a b)).symm ≪≫ CategoryTheory.asIso (t.eTruncLTGELTSelfToGELT a b)