@phdthesis{THESE_1926__65__1_0,
     author = {Roussel, Andr\'e},
     title = {Recherches sur le calcul des variations},
     series = {Th\`eses de l'entre-deux-guerres},
     number = {65},
     year = {1926},
     language = {fr},
     url = {http://archive.numdam.org/item/THESE_1926__65__1_0/}
}