Alphabeta Math
DefinitionDefinition: Literature-sourcedProof: Not applicablePipeline-generatedaudited 2026-09-22
How statement and proof provenance work

The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.

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  • AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
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Skeletal filtration for generalized cohomology

Definition

Let X be a finite CW complex with skeleta Xp, and let h be the CW-pair cohomology theory associated with a reduced generalized cohomology theory h~ by Reduced and unreduced generalized cohomology theories correspond. Use the conventions Xp=(p<0),Xp=X(pdimX), so that X1=. The skeletal filtration of hn(X) is the decreasing filtration Fphn(X):=ker(hn(X)hn(Xp1)),pZ.

By the long exact sequence (LES) of the pair (X,Xp1) and the fact that a relative group maps onto the kernel of the restriction, the same subgroup is Fphn(X)=im(hn(X,Xp1)hn(X)), the image being the kernel of the next restriction by exactness. The filtration is decreasing, Fp+1hn(X)Fphn(X), because the restriction to Xp1 factors through the restriction to Xp. For a finite CW complex it is bounded and exhaustive: Fphn(X)=hn(X) for p0, since hn()=0, and Fphn(X)=0 for p>dimX, since then Xp1=X and the restriction is the identity. No completeness or infinite dimension is asserted.

Source notes

Compare Loizides, §3, printed pp. 4–7, where for a finite CW complex the filtration is written Fmhn(X)=ker(hn(X)hn(Xm)), the indexing here being shifted by one so that Fphn(X) corresponds to the classes vanishing on the (p1)-skeleton; see also Theorem 3.4 and Remark 3.5 there.

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