TY  - JOUR
AU  - N. I. Vulpe
TI  - Affine-invariant conditions for topological distinction of quadratic systems in the presence of a center
JO  - Differencialʹnye uravneniâ
PY  - 1983
SP  - 371
EP  - 379
VL  - 19
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/DE_1983_19_3_a0/
LA  - ru
ID  - DE_1983_19_3_a0
ER  -