@article{CMH_1961__36_139238,
     author = {Guido B\"achli},
     title = {\"Uber die {Integrierbarkeit} von {Systemen} partieller, nichtlinearer {Differentialgleichungen} erster {Ordnung.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {245--264},
     publisher = {mathdoc},
     volume = {36},
     year = {1961},
     zbl = {0107.30003},
     url = {http://geodesic.mathdoc.fr/item/CMH_1961__36_139238/}
}