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Normal Stiefel-Whitney and Pontryagin classes of a closed manifold
Definition
Assume AC. Let be a closed smooth -manifold and choose a stable normal inverse of , which exists by An embedding into Euclidean space gives a rank-(n-m) stable normal inverse ( implies the required countable choice by AC implies DC implies countable choice, and the embedding lemma applies to closed ). Define the total normal Stiefel-Whitney class and the total normal Pontryagin class by with components and (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 and, for connected , the classes are independent of the chosen inverse, so the definition is well posed; equivalently and are the explicit inverses realized by any inverse bundle. For a disconnected closed 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.
Depends on
- Stable normal inverse of the tangent bundle
- An embedding into Euclidean space gives a rank-(n-m) stable normal inverse
- The normal Stiefel-Whitney class is the multiplicative inverse of the tangent class
- The normal Pontryagin class is the rational inverse of the tangent Pontryagin class
- Stiefel–Whitney classes from the projective-bundle relation
- Pontryagin classes by complexification
- Singular cohomology ring
- AC implies DC implies countable choice
- The Axiom of Choice
Used by
- Embedding obstructions include all immersion normal-class obstructions Corollary
- High normal Pontryagin classes obstruct low-codimension immersions Corollary
- High normal Stiefel-Whitney classes obstruct low-codimension immersions Corollary
- Vanishing stable characteristic classes do not make two embeddings isotopic Counterexample
- Normal-class calculation for real projective space Example
- The normal line of an oriented hypersurface is trivial Example
- Parallelizable manifolds have no stable characteristic-class obstruction to Euclidean immersion Proposition
- Real projective space Stiefel-Whitney non-immersion obstruction Theorem
Dependency tree · two levels
45 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Arkadiy Skopenkov, Embedding and Knotting of Manifolds in Euclidean Spaces (arXiv:math/0604045) (standard reference, not scraped)
- John W. Milnor and James D. Stasheff, Characteristic Classes (Annals of Mathematics Studies 74, Princeton University Press; complete text) (standard reference, not scraped)
- Ralph L. Cohen, Immersions of Manifolds and Homotopy Theory (lecture notes, 30 June 2022; complete 46-page text) (standard reference, not scraped)