@article{JMPA_1928_9_7__173_0,
     author = {de Donder, Th.},
     title = {Sur les \'equations lin\'eaires aux d\'eriv\'ees partielles d'un ordre quelconque},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {173--187},
     publisher = {Gauthier-Villars},
     volume = {9e s{\'e}rie, 7},
     year = {1928},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1928_9_7__173_0/}
}