@article{MZ_1964__86_170347,
     author = {Hans G\"unzler},
     title = {Ein {Identit\"atssatz} f\"ur {L\"osungen} quasilinearer hyperbolischer {Differentialgleichungen.}},
     journal = {Mathematische Zeitschrift},
     pages = {337--360},
     publisher = {mathdoc},
     volume = {86},
     year = {1964},
     zbl = {0173.37303},
     url = {http://geodesic.mathdoc.fr/item/MZ_1964__86_170347/}
}