@article{JMPA_1936_9_15__333_0,
     author = {Hadamard, J.},
     title = {La caustique des enveloppes \`a deux param\`etres},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {333--337},
     publisher = {Gauthier-Villars},
     volume = {9e s{\'e}rie, 15},
     year = {1936},
     zbl = {0015.12303},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1936_9_15__333_0/}
}