ABSTRACT
As a mathematical theory, knot theory appeared at the end of the 18th century. It should be emphasised that for more than two hundred years knot theory was studied by A. T. Vandermonde, C.-F. Gauss, F. Klein, and M. Dehn. Systematic study of knot theory begins at the end of the 19th century, when mathematicians and physicists started to tabulate knots. A very interesting idea belonged to W. Thompson. He thought that knots should correspond to chemical elements. However, the most significant results in knot theory took place in the second part of the 20th century. Knot theory originates from a beautiful and quite simple topological problem. Knot theory is rapidly developing; it stimulates constructions of new branches of mathematics. One of the most important branches of knot theory is the theory of virtual knots which is a combinatorial notion proposed by Louis H. Kauffman in 1996.
