1. hairy ball A result in topology stating that a continuous vector field on a sphere is always zero somewhere. The name comes from the fact that you cant flatten all the hair on a hairy ball, like a tennis ball, there will always be a tuft somewhere where the tangential projection of the hair is zero. An immediate corollary to this theorem is that for any continuous map f of the sphere into itself there is a point x such that fx=x or fx is the antipode of x. Another corollary is that at any moment somewhere on the Earth there is no wind.
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