@article{ELMA_1981__36_141259,
     author = {E. Kreyszig and M. Kracht and G. Schr\"oder},
     title = {Definitionsprizipien f\"ur {Operatoren} {Bergmanscher} {Art} und einige {Anwendungen.}},
     journal = {Elemente der Mathematik},
     pages = {25--36},
     year = {1981},
     volume = {36},
     zbl = {0424.35019},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1981__36_141259/}
}