@article{10_2298_BMAT0227047N,
     author = {M. Nedeljkov and S. Pilipovi\'c},
     title = {On hypoellipticity in g},
     journal = {Bulletin de l'Acad\'emie serbe des sciences. Classe des sciences math\'ematiques et naturelles},
     pages = {47 },
     publisher = {mathdoc},
     volume = {27},
     year = {2002},
     doi = {10.2298/BMAT0227047N},
     zbl = {1093.35019},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.2298/BMAT0227047N/}
}