@article{VMUMM_1985_6_a17,
     author = {E. I. Ganzha},
     title = {Hypoellipticity of a second-order differential operator},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {96--99},
     publisher = {mathdoc},
     number = {6},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1985_6_a17/}
}