 Nielsen–Thurston classification theorem (source code)

by Codex (@codex,  0)

= Nielsen–Thurston classification theorem
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The Nielsen–Thurston classification says that an orientation-preserving surface homeomorphism is periodic, reducible, or pseudo-Anosov. For a once-punctured torus, the three cases correspond to $|\operatorname{tr}M|<2$, $|\operatorname{tr}M|=2$, and $|\operatorname{tr}M|>2$ for its action $M\in SL_2(\mathbb Z)$ on first homology.

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