To install click the Add extension button. That's it.

The source code for the WIKI 2 extension is being checked by specialists of the Mozilla Foundation, Google, and Apple. You could also do it yourself at any point in time.

Kelly Slayton
Congratulations on this excellent venture… what a great idea!
Alexander Grigorievskiy
I use WIKI 2 every day and almost forgot how the original Wikipedia looks like.
Live Statistics
English Articles
Improved in 24 Hours
Added in 24 Hours
What we do. Every page goes through several hundred of perfecting techniques; in live mode. Quite the same Wikipedia. Just better.

From Wikipedia, the free encyclopedia

Perko pair
Arf invariant 1
Braid length 10
Braid no. 3
Bridge no. 3
Crosscap no. 2
Crossing no. 10
Genus 3
Hyperbolic volume 5.63877
Unknotting no. 3
Conway notation [3:-20:-20]
A-B notation 10161/10162
Dowker notation 4, 12, -16, 14, -18, 2, 8, -20, -10, -6
Last /Next 10<sub>160</sub> / 10<sub>162</sub>
hyperbolic, fibered, prime, reversible

In the mathematical theory of knots, the Perko pair, named after Kenneth Perko, is a pair of entries in classical knot tables that actually represent the same knot. In Rolfsen's knot table, this supposed pair of distinct knots is labeled 10161 and 10162. In 1973, while working to complete the Tait–Little knot tables of knots up to 10 crossings (dating from the late 19th century),[1] Perko found the duplication in C. N. Little's table.[2] This duplication had been missed by John Horton Conway several years before in his knot table and subsequently found its way into Rolfsen's table.[3] The Perko pair gives a counterexample to a "theorem" claimed by Little in 1900 that the writhe of a reduced diagram of a knot is an invariant (see Tait conjectures), as the two diagrams for the pair have different writhes.

In some later knot tables, the knots have been renumbered slightly (knots 10163 to 10166 are renumbered as 10162 to 10165) so that knots 10161 and 10162 are different. Some authors have mistaken these two renumbered knots for the Perko pair and claimed incorrectly that they are the same.[4]


  1. ^ C.N. Little, Non-alternating +/- knots, Trans. Roy. Soc. Edinburgh 39 (1900), page 774.
  2. ^ Kenneth A. Perko Jr.(b.1943), On the classification of knots. Proc. Amer. Math. Soc. 45 (1974), 262—266.
  3. ^ Dale Rolfsen, Knots and Links (see Appendix C for the knot table), 1976, ISBN 0-914098-16-0.
  4. ^ "The Revenge of the Perko Pair", Accessed February 2016. Richard Elwes points out a common mistake in describing the Perko pair.

External links

This page was last edited on 20 August 2017, at 20:18.
Basis of this page is in Wikipedia. Text is available under the CC BY-SA 3.0 Unported License. Non-text media are available under their specified licenses. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. WIKI 2 is an independent company and has no affiliation with Wikimedia Foundation.