@article{EJDE_2011__2011__a4,
     author = {Bendjeddou,  Ahmed and Cheurfa,  Rachid},
     title = {Cubic and quartic planar differential systems with exact algebraic limit cycles},
     journal = {Electronic journal of differential equations},
     year = {2011},
     volume = {2011},
     zbl = {1211.34042},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2011__2011__a4/}
}