@article{MZ_1977__156_172578,
     author = {Rainer Picard},
     title = {Zur {Existenz} des {Wellenoperators} bei {Anfangsrandwertproblemen} vom {Maxwell-Typ.}},
     journal = {Mathematische Zeitschrift},
     pages = {175--186},
     publisher = {mathdoc},
     volume = {156},
     year = {1977},
     zbl = {0346.35087},
     url = {http://geodesic.mathdoc.fr/item/MZ_1977__156_172578/}
}