@article{02142909,
title = {A group-free characterization of the },
journal = {Advances in Geometry},
volume = {4},
year = {2004},
pages = {141-164},
doi = {10.1515/advg.2004.011},
zbl = {1068.51007},
language = {en},
url = {http://dml.mathdoc.fr/item/02142909}
}
Cooperstein, Bruce N.; Shpectorov, Sergey V. A group-free characterization of the . Advances in Geometry, Tome 4 (2004) pp. 141-164. doi : 10.1515/advg.2004.011. http://gdmltest.u-ga.fr/item/02142909/