The Augmentation Subgroup of a Link E. BrownR. Crowell Indiana University Mathematics Journal 1966 text pdf 10.1512/iumj.1966.15.15072 10.1512/iumj.1966.15.15072 en Indiana Univ. Math. J. 15 (1966) 1065 - 1074 state-of-the-art mathematics http://iumj.org/access/