@article{PORMA_1966__25_2_114978,
     author = {Stein, F. Max},
     title = {A note on families of singular {Sturm-Liouville} systems},
     journal = {Portugaliae mathematica},
     pages = {91--98},
     publisher = {mathdoc},
     volume = {25},
     number = {2},
     year = {1966},
     mrnumber = {0209550},
     zbl = {0146.29703},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1966__25_2_114978/}
}