@article{ASENS_1968_4_1_3_417_0,
     author = {Goldschmidt, Hubert},
     title = {Prolongations of linear partial differential equations. {I.} {A} conjecture of {\'Elie} {Cartan}},
     journal = {Annales scientifiques de l'\'Ecole Normale Sup\'erieure},
     pages = {417--444},
     publisher = {Elsevier},
     volume = {Ser. 4, 1},
     number = {3},
     year = {1968},
     doi = {10.24033/asens.1168},
     mrnumber = {38 #3888},
     zbl = {0167.09402},
     language = {en},
     url = {http://www.numdam.org/articles/10.24033/asens.1168/}
}