@article{EJDE_2004__2004__a69,
     author = {Guzman,  Adolfo W.},
     title = {Structural stability of polynomial second order differential equations with periodic coefficients},
     journal = {Electronic journal of differential equations},
     year = {2004},
     volume = {2004},
     zbl = {1053.37009},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2004__2004__a69/}
}