@article{BASS_2002_27_1_a3,
     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 - 56},
     publisher = {mathdoc},
     volume = {27},
     number = {1},
     year = {2002},
     zbl = {1093.35019},
     url = {http://geodesic.mathdoc.fr/item/BASS_2002_27_1_a3/}
}