@article{DAN_1992_323_4_a2,
     author = {A. Dzhuraev},
     title = {Degenerate systems of first-order partial differential systems},
     journal = {Doklady Akademii Nauk},
     pages = {623--627},
     publisher = {mathdoc},
     volume = {323},
     number = {4},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1992_323_4_a2/}
}