New presentations of a link and virtual link
Abstract
An embedding presentation of a diagram is introduced, which has proved to be a unique presentation of a diagram. Let ℒ be a set of all diagrams, called also links in this paper. An algebraic system (ℒ,∼) is constructed. In fact, a link in R3 (or S3) is the equivalent class [L] where L is one of its embedding presentations. Based on (ℒ,∼), Reduction Crossing Algorithm is proposed which is used to reduce the number of crossings in an embedding presentation by introducing a main tool called a pass replacement. For an infinite set of unknots 𝒰, each K in 𝒰 can be transformed into the trivial unknot in at most O(nc) by applying the algorithm where c is a constant, K∈𝒰 and n=|V(K)|. As special consequences, three unknots are unknotted, which are Goeritz’s unknot, Thistlethwaite’s unknot and Haken’s unknot (image courtesy of Cameron Gordon). Moreover, an infinite family of unknots KG2k,2l∈𝒰 are unknotted in O(nloglogn) time. In addition, unique presentations of a virtual link, an oriented link and oriented virtual link are introduced, respectively.