TY  - JOUR
AU  - V. S. Vinogradov
TI  - 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
JO  - Doklady Akademii Nauk
PY  - 1981
SP  - 1043
EP  - 1046
VL  - 260
IS  - 5
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DAN_1981_260_5_a3/
LA  - ru
ID  - DAN_1981_260_5_a3
ER  -