TY  - JOUR
AU  - A. V. Skitovich
TI  - Conditions for the occurrence of the problem of center and focus
JO  - Differencialʹnye uravneniâ
PY  - 1977
SP  - 1061
EP  - 1069
VL  - 13
IS  - 6
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1977_13_6_a10/
LA  - ru
ID  - DE_1977_13_6_a10
ER  -