@article{MZ_1963__81_170136,
     author = {Heinz-Otto Kreiss},
     title = {\"Uber ein {St\"orungsproblem} f\"ur partielle {Differentialgleichungen.}},
     journal = {Mathematische Zeitschrift},
     pages = {35--45},
     publisher = {mathdoc},
     volume = {81},
     year = {1963},
     zbl = {0156.33701},
     url = {http://geodesic.mathdoc.fr/item/MZ_1963__81_170136/}
}