@article{CMUC_1980_21_1_a11,
     author = {Dr\'abek, Pavel},
     title = {Remarks on multiple periodic solutions of nonlinear ordinary differential equations},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {155--160},
     year = {1980},
     volume = {21},
     number = {1},
     mrnumber = {566247},
     zbl = {0425.34042},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1980_21_1_a11/}
}