@article{CMH_1961__36_139239,
     author = {Bruno Scarpellini},
     title = {Approximation von {Funktionen} durch {Linearkombinationen} von {Eigenfunktionen} {STURM-LIOUVILLEscher} {Differentialgleichungen.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {265--305},
     publisher = {mathdoc},
     volume = {36},
     year = {1961},
     zbl = {0109.29101},
     url = {http://geodesic.mathdoc.fr/item/CMH_1961__36_139239/}
}