1. Hopf Algebras;Abe,1977
2. On the Vassiliev knot invariants;Bar-Natan;Topology,1995
3. Finite type invariants of ribbon 2-knots;Habiro,1999
4. On the Alexander polynomials of 2-spheres in a 4-sphere;Kinoshita;Ann. of Math. (2),1954
5. Stable equivalence of ribbon presentations;Marumoto;J. Knot Theory Ramifications,1992