Self Linking Numbers of Space Polygons T. Banchoff Indiana University Mathematics Journal 1976 text pdf 10.1512/iumj.1976.25.25093 10.1512/iumj.1976.25.25093 en Indiana Univ. Math. J. 25 (1976) 1171 - 1188 state-of-the-art mathematics http://iumj.org/access/