@article{MAN_1986__275_164143,
     author = {J. Rohlfs and G.A. Margulis},
     title = {On the {Proportionality} of {Covolumes} of {Discrete} {Subgroups.}},
     journal = {Mathematische Annalen},
     pages = {197--206},
     publisher = {mathdoc},
     volume = {275},
     year = {1986},
     zbl = {0579.22014},
     url = {http://geodesic.mathdoc.fr/item/MAN_1986__275_164143/}
}