The spectrum of elliptic axial distances in Kleinian groups F. GehringT. MarshallGaven Martin Indiana University Mathematics Journal 1998 text pdf 10.1512/iumj.1998.47.1433 10.1512/iumj.1998.47.1433 en Indiana Univ. Math. J. 47 (1998) 1 - 10 state-of-the-art mathematics http://iumj.org/access/