Borsuk-Ulam theorem (source code)

= Borsuk-Ulam theorem
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Every continuous map $f:S^n\to\mathbb R^n$ takes the same value at some antipodal pair. Equivalently, every continuous antipodal map $S^n\to\mathbb R^n$ has a zero, and there is no antipodal map $S^n\to S^{n-1}$.