@article{AIHP_1956__15_2_123_0,
     author = {Cap, F.},
     title = {Le principe de Fermat dans les milieux absorbants non-homog\`enes},
     journal = {Annales de l'institut Henri Poincar\'e},
     pages = {123--131},
     publisher = {INSTITUT HENRI POINCAR\'E ET GAUTHIER-VILLARS},
     volume = {15},
     number = {2},
     year = {1956},
     zbl = {0072.43802},
     mrnumber = {87449},
     language = {fr},
     url = {www.numdam.org/item/AIHP_1956__15_2_123_0/}
}

Cap, F. Le principe de Fermat dans les milieux absorbants non-homogènes. Annales de l'institut Henri Poincaré, Tome 15 (1956) no. 2, pp. 123-131. http://www.numdam.org/item/AIHP_1956__15_2_123_0/