La courbure totale absolue minimale des surfaces dans E 3 Nicolaas H. Kuiper (1976) Mémoires de la Société Mathématique de France
Link homotopy invariants of graphs in R3. Kouki Taniyama (1994) Revista Matemática de la Universidad Complutense de Madrid In this paper we define a link homotopy invariant of spatial graphs based on the second degree coefficient of the Conway polynomial of a knot.