@phdthesis{THESE_1919__17__1_0,
     author = {Cerf, G.},
     title = {Sur les transformations des \'equations aux d\'eriv\'ees partielles d'ordre quelconque \`a deux variables ind\'ependantes},
     series = {Th\`eses de l'entre-deux-guerres},
     number = {17},
     year = {1919},
     language = {fr},
     url = {http://www.numdam.org/item/THESE_1919__17__1_0/}
}