@article{05029998, title = {On hypoellipticity in }, journal = {Bulletin. Classe des Sciences Math\'ematiques et Naturelles. Sciences Math\'ematiques}, volume = {123}, year = {2002}, pages = {47-56}, doi = {10.2298/BMAT0227047N}, zbl = {1093.35019}, language = {en}, url = {http://dml.mathdoc.fr/item/05029998} }
Nedeljkov, M.; Pilipović, S. On hypoellipticity in . Bulletin. Classe des Sciences Mathématiques et Naturelles. Sciences Mathématiques, Tome 123 (2002) pp. 47-56. doi : 10.2298/BMAT0227047N. http://gdmltest.u-ga.fr/item/05029998/