@article{EJDE_2012__2012__a30,
     author = {Llibre,  Jaume and Makhlouf,  Amar},
     title = {Limit cycles for fourth-order autonomous differential equations},
     journal = {Electronic journal of differential equations},
     year = {2012},
     volume = {2012},
     zbl = {1243.37044},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2012__2012__a30/}
}