@article{EJDE_2014__2014__a151,
     author = {Gine,  Jaume},
     title = {Non-existence of limit cycles for planar vector fields},
     journal = {Electronic journal of differential equations},
     year = {2014},
     volume = {2014},
     zbl = {1295.34043},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2014__2014__a151/}
}