@article{10_4064_ap_16_1_69_94,
     author = {A. Lasota and Z. Opial},
     title = {Sur les solutions p\'eriodiques des \'equations diff\'erentielles ordinaires},
     journal = {Annales Polonici Mathematici},
     pages = {69--94},
     publisher = {mathdoc},
     volume = {16},
     number = {1},
     year = {1964},
     doi = {10.4064/ap-16-1-69-94},
     language = {fr},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-16-1-69-94/}
}