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TauCeti.AlgebraicTopology.Singular.Cubical.Comparison.Relative.Basic

The relative comparison of cubical and simplicial singular chains #

For a topological pair P = (X, A), the relative normalized cubical chain complex P.cubicalChainComplex k is the cokernel of the map of normalized cubical chains induced by the inclusion A → X. This inclusion is injective on normalized chains (NormalizedCubicalChain.map_injective), so the sequence 0 ⟶ N(A) ⟶ N(X) ⟶ N(X, A) ⟶ 0 is short exact (TopPair.shortExact_cubicalChainComplexShortComplex). In each degree it splits, since the push-forward along the inclusion A → X has a left inverse (NormalizedCubicalChain.exists_comp_map_eq_id), so the relative chains are projective modules.

The comparison maps of TauCeti.cubicalSingularHomotopyEquiv are natural, so they carry the chains of A into those of A and induce maps of relative chain complexes in both directions (TopPair.singularToCubicalRel, TopPair.cubicalToSingularRel). By the five lemma, applied to the long exact homology sequences, both are quasi-isomorphisms, so relative cubical homology is relative singular homology (TopPair.singularCubicalHomologyIso), naturally in the pair. Its inverse is induced by TopPair.cubicalToSingularRel, because the natural homotopy between the composite on simplicial chains and the identity descends to relative chains (TopPair.singularToCubicalRelCompHomotopy). The relative homotopy invariance of cubical homology is transported from the simplicial one (TopPair.Homotopy.congr_homologyMap_cubicalChainComplexMap).

Main definitions #

Main results #

References #

The inclusion of a subspace induces a monomorphism of normalized cubical chains.

@[reducible, inline]
noncomputable abbrev TopPair.cubicalChainComplex (k : Type u) [Ring k] (P : TopPair) :

The relative normalized cubical chain complex of a topological pair (X, A): the cokernel of the map of normalized cubical chains induced by the inclusion A → X.

Instances For
    @[simp]

    The chains of the subspace vanish degreewise in the relative normalized cubical chains of a pair.

    @[reducible, inline]

    The sequence N(A) ⟶ N(X) ⟶ N(X, A) of normalized cubical chain complexes of a pair.

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      The normalized cubical chain sequence of a pair is short exact.

      The terms of the relative normalized cubical chain complex of a pair are projective: the chains of the subspace split off the chains of the ambient space (TauCeti.NormalizedCubicalChain.exists_comp_map_eq_id), so the relative chains are a direct summand of the projective chains of the ambient space.

      A normalized cubical n-chain c of the ambient space of a pair (X, A) represents the class μ of the relative cubical homology Hₙ(X, A) when its image in the relative chains is a relative cycle whose class is μ.

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        Every class of the relative cubical homology of a pair is represented by a chain of the ambient space.

        A linear map out of the normalized cubical n-chains of the ambient space of a pair which vanishes on the chains of the subspace, descended to the relative chains (TopPair.cubicalChainComplexXDesc_π).

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          noncomputable def TopPair.cubicalChainComplexMap (k : Type u) [Ring k] {P P' : TopPair} (f : P ⟶ P') :

          The map of relative normalized cubical chains induced by a map of pairs.

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            Singular cubes as relative chains #

            noncomputable def TopPair.cubicalChainOfCube (k : Type u) [Ring k] {P : TopPair} {m : ℕ} (c : TauCeti.SingularCube (↑fst) m) :
            ↑((cubicalChainComplex k P).X m)

            A singular cube of the ambient space of P, as a relative normalized cubical chain of P.

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              @[simp]

              A degenerate cube vanishes as a relative chain.

              @[simp]

              A cube of the subspace vanishes as a relative chain.

              The relative boundary of a cube is the signed sum of the relative chains of its faces.

              theorem TopPair.cubicalChainComplexX_linearMap_ext {k : Type u} [Ring k] {P : TopPair} {n : ℕ} {M : Type u_1} [AddCommGroup M] [Module k M] {f₁ f₂ : ↑((cubicalChainComplex k P).X n) →ₗ[k] M} (h : ∀ (c : TauCeti.SingularCube (↑fst) n), f₁ (cubicalChainOfCube k c) = f₂ (cubicalChainOfCube k c)) :
              f₁ = f₂

              Two linear maps out of the relative normalized cubical n-chains of a pair agree if they agree on the relative chain of every cube.

              theorem TopPair.cubicalChainComplexX_linearMap_ext_iff {k : Type u} [Ring k] {P : TopPair} {n : ℕ} {M : Type u_1} [AddCommGroup M] [Module k M] {f₁ f₂ : ↑((cubicalChainComplex k P).X n) →ₗ[k] M} :
              f₁ = f₂ ↔ ∀ (c : TauCeti.SingularCube (↑fst) n), f₁ (cubicalChainOfCube k c) = f₂ (cubicalChainOfCube k c)
              @[simp]

              The descent of a linear map g to the relative chains takes the relative chain of a cube c to the value of g on the class of c.

              @[simp]

              The chain map induced by a map of pairs f sends the relative chain of a cube c to that of f ∘ c.

              A singular cube sending the boundary of the cube into the subspace is a relative cycle.

              noncomputable def TopPair.cubicalCycleOfCube (k : Type u) [Ring k] {P : TopPair} {m : ℕ} (c : TauCeti.SingularCube (↑fst) (m + 1)) (hc : Set.MapsTo (⇑c) (Cube.boundary (Fin (m + 1))) (Set.range ⇑(CategoryTheory.ConcreteCategory.hom map))) :

              A singular cube sending the boundary of the cube into the subspace, as a relative cycle of the normalized cubical chains of P.

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                The map on cycles induced by a map of pairs f sends the relative cycle of a cube c to that of f ∘ c.

                The boundary of a relative cube #

                The boundary of a relative cube, read in the subspace. A singular cube c of X sending the boundary of the cube into A has its faces in A, and this is the signed sum ∑ᵢ (-1)ⁱ (cᵢ⁰ - cᵢ¹) of these faces as a normalized cubical chain of A. Its image in X is the boundary of c (TopPair.map_cubicalBoundaryChainOfCube).

                Instances For

                  The boundary of a relative cube is the signed sum ∑ᵢ (-1)ⁱ (cᵢ⁰ - cᵢ¹) of its faces, lifted to the subspace.

                  @[simp]

                  The boundary of a relative cube, read in the subspace, is carried to the boundary of the cube by the inclusion of the subspace.

                  @[simp]

                  The boundary of a relative cube, read in the subspace, is a cycle.

                  @[simp]

                  The boundary of a relative cube, read in the subspace, is killed by every differential of the normalized cubical chain complex of the subspace.

                  The boundary of a singular cube c of X sending the boundary of the cube into A, as a normalized cubical cycle of A.

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                    The relative comparison maps #

                    The quotient map from the simplicial singular chains of the ambient space to the relative singular chains, with its source written as (singularChains k).obj P.fst.

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                      The comparison map from relative simplicial to relative cubical chains, induced by singularToCubical.

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                        The comparison map from relative cubical to relative simplicial chains, induced by cubicalToSingular.

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                          The comparison maps as a morphism of short complexes from the simplicial chain sequence of a pair to the cubical one.

                          Instances For

                            The comparison maps as a morphism of short complexes from the cubical chain sequence of a pair to the simplicial one.

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                              The relative comparison maps compose, on relative simplicial chains, to a map chain homotopic to the identity: the natural homotopy singularToCubicalCompHomotopy descends to the quotient by the chains of the subspace.

                              Instances For
                                @[simp]

                                The quotient equation for the homotopy operator on relative simplicial chains.

                                The relative comparison map to cubical chains is a quasi-isomorphism.

                                The relative comparison map to simplicial chains is a quasi-isomorphism.

                                The relative comparison map to cubical chains is natural in the pair.

                                Relative cubical singular homology is relative singular homology.

                                Instances For

                                  The inverse of the relative comparison isomorphism on homology is natural in the pair.

                                  The inverse comparison isomorphisms of absolute and relative homology commute with the maps from absolute to relative homology: an absolute cubical class, read in relative cubical homology and then in relative singular homology, is its image in absolute singular homology read in relative singular homology.

                                  The inverse comparison isomorphisms of absolute and relative homology commute with the maps from absolute to relative homology: an absolute cubical class, read in relative cubical homology and then in relative singular homology, is its image in absolute singular homology read in relative singular homology.

                                  Homotopic maps of pairs induce the same map on relative cubical homology, transported from relative singular homology through the relative comparison.