@article{JMPA_1898_5_4__27_0,
     author = {Hadamard},
     title = {Les surfaces \`a courbures oppos\'ees et leurs lignes g\'eod\'esiques},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {27--73},
     publisher = {Gauthier-Villars},
     volume = {5e s{\'e}rie, 4},
     year = {1898},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1898_5_4__27_0/}
}