TY  - JOUR
AU  - S. D. Shchuko
TI  - On the problem of distinguishing between a center and a focus
JO  - Doklady Akademii Nauk
PY  - 1972
SP  - 1008
EP  - 1010
VL  - 203
IS  - 5
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DAN_1972_203_5_a8/
LA  - ru
ID  - DAN_1972_203_5_a8
ER  -