@article{JMPA_1939_9_18__291_0,
     author = {Cerf, G.},
     title = {Les \'equations lin\'eaires aux d\'eriv\'ees partielles et la m\'ethode de la variation des constantes},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {291--302},
     publisher = {Gauthier-Villars},
     volume = {9e s{\'e}rie, 18},
     year = {1939},
     zbl = {0023.03801},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1939_9_18__291_0/}
}