Euler class

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Euler class

  • The Euler class of the tangent bundle of an oriented manifold can be identified with the Euler characteristic times the fundamental class

  • Fact: \(\widehat{{\mathbf{T}}}S^2 \underset{\operatorname{Diff}}{\cong} {\mathbf{RP}}^3\) are diffeomorphic, where the LHS is the unit tangent bundle. attachments/Pasted%20image%2020220403210801.png

Relation to BunG: attachments/Pasted%20image%2020220403210833.png

attachments/Pasted%20image%2020220403193727.png attachments/Pasted%20image%2020220403193822.png

Relation to the Gysin sequence: attachments/Pasted%20image%2020220403193844.png

attachments/Pasted%20image%2020220403193904.png

attachments/Pasted%20image%2020220403193926.png

Formulas

attachments/Pasted%20image%2020220403212713.png attachments/Pasted%20image%2020220403212719.png

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