@article{MAN_1980__247_163351,
     author = {Palle E.T. Jorgensen},
     title = {Partial {Differential} {Operators} and {Discrete} {Subgroups} of a {Lie} {Group.}},
     journal = {Mathematische Annalen},
     pages = {101--110},
     publisher = {mathdoc},
     volume = {247},
     year = {1980},
     zbl = {0433.22010},
     url = {http://geodesic.mathdoc.fr/item/MAN_1980__247_163351/}
}