@article{1250127497,
author = {Perko, L.M.},
title = {Limit cycles of quadratic systems in the plane},
journal = {Rocky Mountain J. Math.},
volume = {14},
number = {4},
year = {1984},
pages = { 619-646},
language = {en},
url = {http://dml.mathdoc.fr/item/1250127497}
}
Perko, L.M. Limit cycles of quadratic systems in the plane. Rocky Mountain J. Math., Tome 14 (1984) no. 4, pp. 619-646. http://gdmltest.u-ga.fr/item/1250127497/