@article{MZ_1920__7_167579,
     author = {R., Courant},
     title = {\"Uber die {Eigenwerte} bei den {Differentialgleichungen} der mathe-matischen {Physik}},
     journal = {Mathematische Zeitschrift},
     pages = {1--57},
     publisher = {mathdoc},
     volume = {7},
     year = {1920},
     zbl = {47.0455.02},
     url = {http://geodesic.mathdoc.fr/item/MZ_1920__7_167579/}
}