@article{DAN_1978_238_1_a4,
     author = {Le Khyu Zien and V. I. Shevchenko},
     title = {Homotopy classification of {Petrovskii} elliptic systems of equations in the plane},
     journal = {Doklady Akademii Nauk},
     pages = {26--28},
     publisher = {mathdoc},
     volume = {238},
     number = {1},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1978_238_1_a4/}
}