@book{MSM_1937__84__R3_0,
     author = {Freda, H\'el\`ene},
     title = {M\'ethode des caract\'eristiques pour l'int\'egration des \'equations aux d\'eriv\'ees partielles lin\'eaires hyperboliques},
     series = {M\'emorial des sciences math\'ematiques},
     publisher = {Gauthier-Villars},
     number = {84},
     year = {1937},
     language = {fr},
     url = {http://archive.numdam.org/item/MSM_1937__84__R3_0/}
}