| 词条 | 2-bridge knot |
| 释义 |
| perrow = 2 | width = 60 | header = Bridge number 2 | image1 = 2-bridge trefoil.svg | caption1 = 31 | image2 = Blue Cinquefoil Knot.png | caption2= 51 | image3 = Blue 6 3 Knot.png | caption3 = 63 | image4 = Blue 7 1 Knot.png | caption4 = 71... }} 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 {{lang|de|Viergeflechte}} ({{Language with name/for||German|four braids}}). 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
External links
1 : 2 bridge number knots and links |
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