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DefinitionDefinition: Literature-sourcedProof: Not applicablePipeline-generatedjudge pass (gpt-6.1-sol)
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.

  • Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
  • AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
  • AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.

These labels describe origin, not correctness: citations and verification chips remain separate evidence.

Normal Stiefel-Whitney and Pontryagin classes of a closed manifold

Definition

Assume AC. Let M be a closed smooth m-manifold and choose a stable normal inverse (ν,φ) of M, which exists by An embedding into Euclidean space gives a rank-(n-m) stable normal inverse (AC implies the required countable choice by AC implies DC implies countable choice, and the embedding lemma applies to closed M). Define the total normal Stiefel-Whitney class and the total normal Pontryagin class by wˉ(M):=w(ν)∈H∗(M;F2),pˉ(M):=p(ν)∈H∗(M;Q), with components wˉi(M)∈Hi(M;F2) and pˉi(M)∈H4i(M;Q) (Stiefel–Whitney classes from the projective-bundle relation, Pontryagin classes by complexification, Singular cohomology ring). By The normal Stiefel-Whitney class is the multiplicative inverse of the tangent class and The normal Pontryagin class is the rational inverse of the tangent Pontryagin class the classes wˉi(M) and, for connected M, the classes pˉi(M) are independent of the chosen inverse, so the definition is well posed; equivalently wˉ(M)=w(TM)−1 and pˉ(M)=p(TM)−1 are the explicit inverses realized by any inverse bundle. For a disconnected closed M the Pontryagin definition is applied componentwise. These are the classes also called the normal, dual, or (in Skopenkov's terminology) Stiefel-Whitney and Pontryagin classes of the manifold; they are the classes read by the immersion and embedding tests of this page.

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