@article{JMPA_1936_9_15__177_0,
     author = {Janet, Maurice},
     title = {Dualit\'e dans certaines questions de calcul des variations},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {177--191},
     publisher = {Gauthier-Villars},
     volume = {9e s{\'e}rie, 15},
     year = {1936},
     zbl = {0014.21902},
     language = {fr},
     url = {http://archive.numdam.org/item/JMPA_1936_9_15__177_0/}
}