@article{JMPA_1842_1_7__55_0,
     author = {Bertrand, J.},
     title = {Note sur un point du calcul des variations},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {55--58},
     publisher = {Gauthier-Villars},
     volume = {1e s{\'e}rie, 7},
     year = {1842},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1842_1_7__55_0/}
}