@article{DAN_1990_314_5_a7,
     author = {Yu. V. Egorov and Nguen Min' Chi},
     title = {Maximally hypoelliptic operators with a noninvolutive
},
     journal = {Doklady Akademii Nauk},
     pages = {1059--1061},
     publisher = {mathdoc},
     volume = {314},
     number = {5},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1990_314_5_a7/}
}