TWIN GROUPS OF VIRTUAL 2-BRIDGE KNOTS AND ALMOST CLASSICAL KNOTS
Abstract
Every virtual knot has a pair of groups called the upper and lower groups of the knot. In this paper we treat two topics on those groups: We first give a sufficient condition for a pair of groups which are realized by a certain virtual knot as the upper and lower groups. Secondly we give a necessary condition for a virtual knot to be almost classical in terms of the first elementary ideals of the groups.