%0 Journal Article
%A E. M. Landis
%A I. G. Petrovskii
%T On the number of limit cycles of equation $\frac{dy}{dx}=\frac{P(x,y)}{Q(x,y)}$, in which~$P$ and~$Q$ 

%J Doklady Akademii Nauk
%D 1957
%P 748-751
%V 113
%N 4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DAN_1957_113_4_a6/
%G ru
%F DAN_1957_113_4_a6