- 2-bridge knot
In

mathematics , 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.Other names for 2-bridge knots are

**rational knots**,**4-plats**, and**Viergeflechte**. 2-bridge links are defined similarly as above, but each component will have one min and max. 2-bridge knots were classified by Seifert, using the fact that the 2-sheeted branched cover of the3-sphere over the knot is alens space .The names rational knot and

**rational link**were coined by John Conway who defined them as arising from numerator closures ofrational tangle s.**ee also***

bridge number **External links*** [

*http://www.tcs.ifi.lmu.de/~gruberh/ Table and invariants of rational knots with up to 16 crossings*]

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