@article{10_4064_ap_7_3_241_246,
     author = {Z. Opial},
     title = {D\'emonstration d'un th\'eor\`eme de {N.} {Levinson} et {C.} {Langenhop}},
     journal = {Annales Polonici Mathematici},
     pages = {241--246},
     publisher = {mathdoc},
     volume = {7},
     number = {3},
     year = {1959},
     doi = {10.4064/ap-7-3-241-246},
     language = {fr},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/ap-7-3-241-246/}
}