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Mathlib.Algebra.Homology.Embedding.StupidTrunc

The stupid truncation of homological complexes #

Given an embedding e : c.Embedding c' of complex shapes, we define a functor stupidTruncFunctor : HomologicalComplex C c' ⥤ HomologicalComplex C c' which sends K to K.stupidTrunc e which is defined as (K.restriction e).extend e.

@[implicit_reducible]

The stupid truncation of a complex K : HomologicalComplex C c' relatively to an embedding e : c.Embedding c' of complex shapes.

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    noncomputable def HomologicalComplex.stupidTruncXIso {ι : Type u_1} {ι' : Type u_2} {c : ComplexShape ι} {c' : ComplexShape ι'} {C : Type u_3} [CategoryTheory.Category.{v_1, u_3} C] [CategoryTheory.Limits.HasZeroMorphisms C] [CategoryTheory.Limits.HasZeroObject C] (K : HomologicalComplex C c') (e : c.Embedding c') [e.IsRelIff] {i : ι} {i' : ι'} (hi' : e.f i = i') :
    (K.stupidTrunc e).X i' ≅ K.X i'

    The isomorphism (K.stupidTrunc e).X i' ≅ K.X i' when i is in the image of e.f.

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      theorem HomologicalComplex.congr_stupidTruncXIso {ι : Type u_1} {ι' : Type u_2} {c : ComplexShape ι} {c' : ComplexShape ι'} {C : Type u_3} [CategoryTheory.Category.{v_1, u_3} C] [CategoryTheory.Limits.HasZeroMorphisms C] [CategoryTheory.Limits.HasZeroObject C] (K : HomologicalComplex C c') (e : c.Embedding c') [e.IsRelIff] {i₁ i₂ : ι} {i' : ι'} (hi₁ : e.f i₁ = i') (hi₂ : e.f i₂ = i') :
      K.stupidTruncXIso e hi₁ = K.stupidTruncXIso e hi₂

      The morphism K.stupidTrunc e ⟶ L.stupidTrunc e induced by a morphism K ⟶ L.

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        Auxiliary definition for ιStupidTrunc.

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          The monomorphism K.stupidTrunc e ⟶ K when the embedding e of complex shapes satisfies e.IsTruncGE.

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            Auxiliary definition for πStupidTrunc.

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              The epimorphism K ⟶ K.stupidTrunc e when the embedding e of complex shapes satisfies e.IsTruncLE.

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                @[implicit_reducible]

                The stupid truncation functor HomologicalComplex C c' ⥤ HomologicalComplex C c' given by an embedding e : Embedding c c' of complex shapes.

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                  When e : Embedding c c' satisfies [e.IsTruncGE], this is the natural transformation K.ιStupidTrunc e : K.stupidTrunc e ⟶ K for all K : HomologicalComplex C c'.

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                    When e : Embedding c c' satisfies [e.IsTruncLE], this is the natural transformation K.πStupidTrunc e : K ⟶ K.stupidTrunc e for all K : HomologicalComplex C c'.

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