@article{BSMF_1927__55__89_0,
     author = {Janet, M.},
     title = {Sur la composition des expressions diff\'erentielles lin\'eaires et une application \`a la th\'eorie des syst\`emes d'\'equations aux d\'eriv\'ees partielles},
     journal = {Bulletin de la Soci\'et\'e Math\'ematique de France},
     pages = {89--91},
     publisher = {Soci\'et\'e math\'ematique de France},
     volume = {55},
     year = {1927},
     doi = {10.24033/bsmf.1110},
     language = {fr},
     url = {http://www.numdam.org/articles/10.24033/bsmf.1110/}
}