@article{AFM_2001_26_1_a1,
     author = {Ruth Kellerhals},
     title = {Collars in {PSL(2,H)}},
     journal = {Annales Fennici Mathematici},
     pages = {51--72},
     publisher = {mathdoc},
     volume = {26},
     number = {1},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AFM_2001_26_1_a1/}
}