@article{DAN_1981_260_5_a3,
     author = {V. S. Vinogradov},
     title = {The geometric meaning of the condition of ellipticity of a system of first order differential equations in the plane and its reduction to a complex special form},
     journal = {Doklady Akademii Nauk},
     pages = {1043--1046},
     publisher = {mathdoc},
     volume = {260},
     number = {5},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1981_260_5_a3/}
}