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Hairy ball theorem - Wikipedia, the free encyclopedia |
 | | Since the Betti numbers of a 2-sphere are 1, 0, 1, 0, 0,... |
 | | the Lefschetz number (total trace on homology) of the identity mapping is 2. |
 | | The difference in even and odd dimension is that the Betti numbers of the m-sphere are 0 except in dimensions 0 and m. |
| en.wikipedia.org /wiki/Hairy_ball_theorem (868 words) |
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