The Self-Linking Number of a Closed Space Curve William Pohl Indiana University Mathematics Journal 1968 text pdf 10.1512/iumj.1968.17.17060 10.1512/iumj.1968.17.17060 en Indiana Univ. Math. J. 17 (1968) 975 - 985 state-of-the-art mathematics http://iumj.org/access/