@article{MZ_1973__131_171884,
     author = {Konrad J\"orgens and Joachim Weidmann},
     title = {Zur {Existenz} der {Wellenoperatoren.}},
     journal = {Mathematische Zeitschrift},
     pages = {141--152},
     publisher = {mathdoc},
     volume = {131},
     year = {1973},
     zbl = {0252.35061},
     url = {http://geodesic.mathdoc.fr/item/MZ_1973__131_171884/}
}