@article{MZ_1973__130_171875,
     author = {Hans Wittich and G\"unter Frank},
     title = {Zur {Theorie} linearer {Differenatialgleichungen} im {Komplexen.}},
     journal = {Mathematische Zeitschrift},
     pages = {363--370},
     publisher = {mathdoc},
     volume = {130},
     year = {1973},
     zbl = {0242.34003},
     url = {http://geodesic.mathdoc.fr/item/MZ_1973__130_171875/}
}