@article{GDZPPN002061139, title = {Corners and Arithmetic Groups}, journal = {Commentarii mathematici Helvetici}, volume = {48}, year = {1973}, pages = {436-483}, zbl = {0274.22011}, url = {http://dml.mathdoc.fr/item/GDZPPN002061139} }
Borel, A.; Serre, J-P. Corners and Arithmetic Groups. Commentarii mathematici Helvetici, Tome 48 (1973) pp. 436-483. http://gdmltest.u-ga.fr/item/GDZPPN002061139/