%0 Journal Article
%A A. P. Sadovskii
%T A solution of the center and focus problem in a special case
%J Differencialʹnye uravneniâ
%D 1968
%P 943-945
%V 4
%N 5
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1968_4_5_a19/
%G ru
%F DE_1968_4_5_a19