@article{PMIHES_1979__50__171_0,
     author = {Sullivan, Dennis},
     title = {The density at infinity of a discrete group of hyperbolic motions},
     journal = {Publications Math\'ematiques de l'IH\'ES},
     pages = {171--202},
     publisher = {Institut des Hautes \'Etudes Scientifiques},
     volume = {50},
     year = {1979},
     mrnumber = {81b:58031},
     zbl = {0439.30034},
     language = {en},
     url = {http://archive.numdam.org/item/PMIHES_1979__50__171_0/}
}