@article{JMPA_1926_9_5__395_0,
     author = {Roussel, Andr\'e},
     title = {Recherches sur le calcul des variations},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {395--462},
     publisher = {Gauthier-Villars},
     volume = {9e s{\'e}rie, 5},
     year = {1926},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1926_9_5__395_0/}
}