@article{VMUMM_1987_3_a21,
     author = {T. Spanily},
     title = {Nonhomogeneous subelliptic operators},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {71--73},
     publisher = {mathdoc},
     number = {3},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1987_3_a21/}
}