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In the mathematical field of knot theory, a 2-bridge knot is a knot which can be isotoped so that the natural height function given by the ''z''-coordinate has only two maxima and two minima as critical points. Equivalently, these are the knots with bridge number 2, the smallest possible bridge number for a nontrivial knot. Other names for 2-bridge knots are rational knots, 4-plats, and ''ドイツ語:Viergeflechte'' (). 2-bridge links are defined similarly as above, but each component will have one min and max. 2-bridge knots were classified by Horst Schubert, using the fact that the 2-sheeted branched cover of the 3-sphere over the knot is a lens space. The names ''rational knot'' and ''rational link'' were coined by John Conway who defined them as arising from numerator closures of rational tangles. ==Further reading== * Horst Schubert: Über Knoten mit zwei Brücken, Mathematische Zeitschrift 65:133–170 (1956). * Louis H. Kauffman, Sofia Lambropoulou: On the classification of rational knots, L' Enseignement Mathématique, 49:357–410 (2003). (preprint available at arxiv.org ) ((Archived ) 2009-05-14). * C. C. Adams, ''The Knot Book: An elementary introduction to the mathematical theory of knots.'' American Mathematical Society, Providence, RI, 2004. xiv+307 pp. ISBN 0-8218-3678-1 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「2-bridge knot」の詳細全文を読む スポンサード リンク
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