@article{CMUC_1988_29_2_a0,
     author = {Dr\'abek, Pavel},
     title = {A resonance problem for nonlinear {Duffing} equation},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {205--215},
     year = {1988},
     volume = {29},
     number = {2},
     mrnumber = {957386},
     zbl = {0646.34051},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1988_29_2_a0/}
}