@article{MZ_1930__31_168177,
     author = {L. Lichtenstein},
     title = {Zum {Sturm-Liouvilleschen} {Problem}},
     journal = {Mathematische Zeitschrift},
     pages = {346--349},
     publisher = {mathdoc},
     volume = {31},
     year = {1930},
     zbl = {55.0259.02},
     url = {http://geodesic.mathdoc.fr/item/MZ_1930__31_168177/}
}