TY  - JOUR
AU  - E. M. Landis
AU  - I. G. Petrovskii
TI  - On the number of limit cycles of equation $\frac{dy}{dx}=\frac{P(x,y)}{Q(x,y)}$, in which~$P$ and~$Q$ 

JO  - Doklady Akademii Nauk
PY  - 1957
SP  - 748
EP  - 751
VL  - 113
IS  - 4
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DAN_1957_113_4_a6/
LA  - ru
ID  - DAN_1957_113_4_a6
ER  -