@article{DAN_1979_244_4_a7,
     author = {Le Khyu Zien and V. I. Shevchenko},
     title = {Homotopy classification of systems in the plane that are elliptic in the sense of {Douglis} and {Nirenberg}},
     journal = {Doklady Akademii Nauk},
     pages = {824--827},
     publisher = {mathdoc},
     volume = {244},
     number = {4},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1979_244_4_a7/}
}