Ribbon-clasp T2-knots and semi-welded knots

Abstract

The notion of ribbon-clasp surface-links is a generalization of ribbon surface-links. It is known that any ribbon [Formula: see text]-knot is presented by a welded knot, and then its knot group is isomorphic to the group of the welded knot. In this paper, we define the group of a semi-welded knot. We show that any ribbon-clasp [Formula: see text]-knot is presented by a semi-welded knot and that the knot group of the ribbon-clasp [Formula: see text]-knot is isomorphic to the group of the semi-welded knot.