* T.Y. Li, and J.A. Yorke, Period Three Implies Chaos, American Mathematical Monthly 82, 985 (1975).https://en.wikipedia.org/wiki/American_Mathematical_Monthly
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* T.Y. Li, and J.A. Yorke, Period Three Implies Chaos, [https://en.wikipedia.org/wiki/American_Mathematical_Monthly American Mathematical Monthly] 82, 985 (1975).