TY  - JOUR
AU  - M. A. Lavrent'ev
AU  - B. V. Shabat
TI  - The geometric properties of solutions of non-linear systems of partial differential equations
JO  - Doklady Akademii Nauk
PY  - 1957
SP  - 810
EP  - 811
VL  - 112
IS  - 5
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DAN_1957_112_5_a6/
LA  - ru
ID  - DAN_1957_112_5_a6
ER  -