@article{RM_1975_30_2_a1,
     author = {Yu. V. Egorov},
     title = {Subelliptic operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {59--118},
     publisher = {mathdoc},
     volume = {30},
     number = {2},
     year = {1975},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1975_30_2_a1/}
}