@article{AUPO_1972__12_1_a0,
     author = {Karim, Rahmi Ibrahim Ibrahim Abdel},
     title = {Note on the periodic solutions of systems of ordinary differential equations},
     journal = {Acta Universitatis Palackianae Olomucensis. Facultas Rerum Naturalium. Mathematica},
     pages = {7--14},
     publisher = {mathdoc},
     volume = {12},
     number = {1},
     year = {1972},
     mrnumber = {0344597},
     zbl = {0394.34032},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AUPO_1972__12_1_a0/}
}