@article{GDZPPN002181509,
title = {Central extensions of groups of Lie type.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {218},
year = {1965},
pages = {174-185},
zbl = {0137.25701},
url = {http://dml.mathdoc.fr/item/GDZPPN002181509}
}
Curtis, Charles W. Central extensions of groups of Lie type.. Journal für die reine und angewandte Mathematik, Tome 218 (1965) pp. 174-185. http://gdmltest.u-ga.fr/item/GDZPPN002181509/