Voir la notice de l'article provenant de la source European Digital Mathematics Library
@article{IM_1972__17_142170, author = {H. Helling}, title = {Diskrete {Untergruppen} von {SL2} {(IR).}}, journal = {Inventiones mathematicae}, pages = {217--230}, publisher = {mathdoc}, volume = {17}, year = {1972}, url = {http://geodesic.mathdoc.fr/item/IM_1972__17_142170/} }
H. Helling. Diskrete Untergruppen von SL2 (IR).. Inventiones mathematicae, Tome 17 (1972), pp. 217-230. http://geodesic.mathdoc.fr/item/IM_1972__17_142170/