@article{MZ_1960__74_169878,
     author = {Harro Heuser},
     title = {Zur {Eigenwertheorie} einer {Klasse} symmetrischer {Operatoren.}},
     journal = {Mathematische Zeitschrift},
     pages = {167--185},
     publisher = {mathdoc},
     volume = {74},
     year = {1960},
     zbl = {0119.32201},
     url = {http://geodesic.mathdoc.fr/item/MZ_1960__74_169878/}
}