@article{MZ_1956__66_169619,
     author = {Alexander Ostrowski},
     title = {Zur {Theorie} der partiellen {Differentialgleichungen} erster {Ordnung.}},
     journal = {Mathematische Zeitschrift},
     pages = {70--87},
     publisher = {mathdoc},
     volume = {66},
     year = {1956},
     zbl = {0071.31001},
     url = {http://geodesic.mathdoc.fr/item/MZ_1956__66_169619/}
}