Three-page embeddings of singular knots
arXiv:math/0309325
Abstract
Construction of a semigroup with 15 generators and 84 relations is given. The center of this semigroup is in one-to-one correspondence with the set of all isotopy classes of non-oriented singular knots (links with finitely many double intersections in general position) in three-dimensional space.
14 pages, 5 figures