I am confused how we can define a rotation number of the map from S^1 to R^3 def... | Hacker News

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		daynthelife 4 months ago \| parent \| context \| favorite \| on: A short proof of the Hairy Ball theorem (2016) [pd... I am confused how we can define a rotation number of the map from S^1 to R^3 defined at the end of the second paragraph. R^3 is nullhomotopic, after all...

ajkjk 4 months ago [–]

I think the idea is that you can't, but we're assuming v doesn't vanish at that point which would imply that it's possible?

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