@article{10_4064_ap_7_3_247_254,
     author = {C. Olech and Z. Opial},
     title = {Sur une in\'egalit\'e diff\'erentielle},
     journal = {Annales Polonici Mathematici},
     pages = {247--254},
     publisher = {mathdoc},
     volume = {7},
     number = {3},
     year = {1959},
     doi = {10.4064/ap-7-3-247-254},
     language = {fr},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-7-3-247-254/}
}