@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/