@article{MAN_1940__117_160043,
     author = {W.L. Chow},
     title = {\"Uber {Systeme} von linearen partiellen {Differentialgleichungen} erster {Ordnung.}},
     journal = {Mathematische Annalen},
     pages = {98--105},
     year = {1940},
     volume = {117},
     zbl = {65.0398.01},
     url = {http://geodesic.mathdoc.fr/item/MAN_1940__117_160043/}
}