Graphs and links

Abstract

In this chapter (Chapter V) we present several results which demonstrate a close connection and useful exchange of ideas between graph theory and knot theory. These disciplines were shown to be related from the time of Tait (if not Listing) but the great flow of ideas started only after Jones discoveries. The first deep relation in this new trend was demonstrated by Morwen Thistlethwaite and we describe several results by him in this Chapter. We also presentresults from two (unpublished) preprints [P-P-0,P-18].In particular, in Section 2, we sketch two generalizations of the Tutte polynomial of graphs or, more precisely, the deletion-contraction method which Tutte polynomial utilize. The first generalization considers, instead of graphs, general objects called setoids or group systems. The second one deals with completion of the expansion of a graph with respect to subgraphs. We are motivated here by finite type invariants of links developed by Vassiliev and Gusarov along the line presented in [P-9] (compare Chapter IX). The dichromatic Hopf algebra, described in Section 2, have its origin in Vassiliev-Gusarov theory mixed with work of G. Carlo-Rota and W. Schmitt. In Section 3 we describe Tait conjecture on alternating link diagrams and apply developed methods to study adequate diagrams. In Section 4 we apply 2-variable Kauffman polynomial to alternating links and prove, in particular, the second Tait conjecture. In Section 5 we analyze the Kauffman polynomial of adequate diagrams. In Section 6 we show how coefficients of Homflypt polynomial can be used to obtain new information on classical knot invariants (e.g. Morton-Franks-Williams inequality). In the last section of Chapter V we discuss almost positive links and our method uses K. Taniyama idea of ordering of knots.