| 释义 |
hairy ball hairy ball (topology)A result in topology stating that a continuousvector field on a sphere is always zero somewhere. The namecomes from the fact that you can't flatten all the hair on ahairy ball, like a tennis ball, there will always be a tuftsomewhere (where the tangential projection of the hair iszero). An immediate corollary to this theorem is that for anycontinuous map f of the sphere into itself there is a pointx such that f(x)=x or f(x) is the antipode of x. Anothercorollary is that at any moment somewhere on the Earth thereis no wind. |