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 #
TopPair.cubicalChainComplex k P: the relative normalized cubical chain complex of a pair.TopPair.cubicalChainComplexMap k f: the chain map induced by a map of pairs.TopPair.IsCubicalRepresentative k c μ: a normalized cubical chain of the ambient space is a relative cycle with relative classμ; every class has one (TopPair.exists_isCubicalRepresentative).TopPair.cubicalChainComplexXDesc k g hg: a linear map out of the chains of the ambient space, vanishing on the chains of the subspace, descended to the relative chains.TopPair.cubicalChainOfCube k c,TopPair.cubicalCycleOfCube k c hc: a singular cube as a relative chain, and as a relative cycle when it sends the boundary of the cube into the subspace. Linear maps out of the relative chains are determined by their values on these (TopPair.cubicalChainComplexX_linearMap_ext).TopPair.cubicalChainComplexMap_f_cubicalChainOfCube,TopPair.cyclesMap_cubicalCycleOfCube: their naturality in maps of pairs, andTopPair.d_cubicalChainOfCube_eq_sum: the relative boundary of a cube is the signed sum of its faces.TopPair.cubicalBoundaryChainOfCube k c hc,TopPair.cubicalBoundaryCycleOfCube k c hc: the boundary of a cube sending the boundary of the cube into the subspace, as a chain and as a cycle of the subspace (TopPair.map_cubicalBoundaryChainOfCube).TopPair.singularToCubicalRel k P,TopPair.cubicalToSingularRel k P: the relative comparison maps.TopPair.singularCubicalHomologyIso k P n: relative cubical homology is relative singular homology.TopPair.singularToCubicalRelCompHomotopy k P: the relative comparison maps compose to a map homotopic to the identity on relative simplicial chains.
Main results #
- The terms of
TopPair.cubicalChainComplex k Pare projectivek-modules (an instance). TopPair.quasiIso_singularToCubicalRel,TopPair.quasiIso_cubicalToSingularRel: the relative comparison maps are quasi-isomorphisms.TopPair.Homotopy.congr_homologyMap_cubicalChainComplexMap: homotopic maps of pairs induce the same map on relative cubical homology.
References #
- W. S. Massey, Singular Homology Theory, GTM 70, Springer, 1980, Chapter VII.
- S. Eilenberg and N. Steenrod, Foundations of Algebraic Topology, Princeton, 1952, Chapters I–III.
The inclusion of a subspace induces a monomorphism of normalized cubical chains.
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
The chains of the subspace vanish degreewise in the relative normalized cubical chains of a pair.
The chains of the subspace vanish degreewise in the relative normalized cubical chains of a pair.
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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The map of relative normalized cubical chains induced by a map of pairs.
Instances For
Singular cubes as relative chains #
A singular cube of the ambient space of P, as a relative normalized cubical chain of P.
Instances For
A degenerate cube vanishes as a relative chain.
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.
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.
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.
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.
A singular cube sending the boundary of the cube into the subspace, as a relative cycle of the
normalized cubical chains of P.
Instances For
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).
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The boundary of a relative cube is the signed sum ∑ᵢ (-1)ⁱ (cᵢ⁰ - cᵢ¹) of its faces, lifted
to the subspace.
The boundary of a relative cube, read in the subspace, is carried to the boundary of the cube by the inclusion of the subspace.
The boundary of a relative cube, read in the subspace, is a cycle.
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.
Instances For
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.
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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.
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The quotient equation for the homotopy operator on relative simplicial chains.
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.
The relative comparison map to cubical chains is natural in the pair.
Relative cubical singular homology is relative singular homology.
Instances For
The relative comparison isomorphism on homology is natural in the pair.
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.