@phdthesis{THESE_1941__239__R1_0,
     author = {Gu\'erard des lauriers},
     title = {Sur les syst\`emes diff\'erentiels du second ordre qui admettent un groupe continu fini de transformations},
     series = {Th\`eses de l'entre-deux-guerres},
     number = {239},
     year = {1941},
     language = {fr},
     url = {http://www.numdam.org/item/THESE_1941__239__R1_0/}
}