@article{JMPA_1929_9_8__197_0,
     author = {Hadamard, J.},
     title = {Le principe de {Huyghens} pour les \'equations \`a trois variables ind\'ependantes},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {197--228},
     publisher = {Gauthier-Villars},
     volume = {9e s{\'e}rie, 8},
     year = {1929},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1929_9_8__197_0/}
}