@article{GDZPPN002042320,
title = {On the number of limit cycles in perturbations of a two dimensional nonlinear differential system.},
journal = {Aequationes mathematicae},
volume = {53},
year = {1997},
pages = {254-274},
zbl = {0871.34018},
url = {http://dml.mathdoc.fr/item/GDZPPN002042320}
}
Hainzl, Josef. On the number of limit cycles in perturbations of a two dimensional nonlinear differential system.. Aequationes mathematicae, Tome 53 (1997) pp. 254-274. http://gdmltest.u-ga.fr/item/GDZPPN002042320/