@article{EJDE_2008__2008__a6,
     author = {Chicone,  Carmen and Felts,  Kenny},
     title = {Non-monotone period functions for impact oscillators},
     journal = {Electronic journal of differential equations},
     year = {2008},
     volume = {2008},
     zbl = {1173.34031},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2008__2008__a6/}
}