@article{JMPA_1899_5_5__351_0,
     author = {Beudon, Jules},
     title = {Sur les syst\`emes d'\'equations aux d\'eriv\'ees partielles analogues aux syst\`emes d'\'equations du premier ordre en involution},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {351--364},
     publisher = {Gauthier-Villars},
     volume = {5e s{\'e}rie, 5},
     year = {1899},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1899_5_5__351_0/}
}