%0 Journal Article
%A A. V. Skitovich
%T Conditions for the occurrence of the problem of center and focus
%J Differencialʹnye uravneniâ
%D 1977
%P 1061-1069
%V 13
%N 6
%I mathdoc
%U http://geodesic.mathdoc.fr/item/DE_1977_13_6_a10/
%G ru
%F DE_1977_13_6_a10