TY  - JOUR
AU  - A. P. Sadovskii
TI  - The problem of center and focus
JO  - Differencialʹnye uravneniâ
PY  - 1968
SP  - 2002
EP  - 2009
VL  - 4
IS  - 11
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1968_4_11_a8/
LA  - ru
ID  - DE_1968_4_11_a8
ER  -