@article{MAT_1968_12_2_a3,
     author = {L. V. H\"ormander},
     title = {Hypoelliptic differential equations of second order},
     journal = {Matematika},
     pages = {88--109},
     publisher = {mathdoc},
     volume = {12},
     number = {2},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1968_12_2_a3/}
}