@book{MSM_1927__21__1_0,
     author = {Janet, Maurice},
     title = {Les syst\`emes d'\'equations aux d\'eriv\'ees partielles},
     series = {M\'emorial des sciences math\'ematiques},
     publisher = {Gauthier-Villars},
     number = {21},
     year = {1927},
     language = {fr},
     url = {http://www.numdam.org/item/MSM_1927__21__1_0/}
}