TY  - JOUR
AU  - A. P. Sadovskii
TI  - On the problem of discrimination of center and focus
JO  - Differencialʹnye uravneniâ
PY  - 1969
SP  - 326
EP  - 330
VL  - 5
IS  - 2
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1969_5_2_a10/
LA  - ru
ID  - DE_1969_5_2_a10
ER  -