@article{10_4064_ap_5_1_77_93,
     author = {Z. Opial},
     title = {Sur l'\'equation diff\'erentielle u'' + a(t)u = 0},
     journal = {Annales Polonici Mathematici},
     pages = {77--93},
     publisher = {mathdoc},
     volume = {5},
     number = {1},
     year = {1958},
     doi = {10.4064/ap-5-1-77-93},
     language = {fr},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-5-1-77-93/}
}