@article{JMPA_1891_4_7__157_0,
     author = {Appell, P.},
     title = {Sur les fonctions p\'eriodiques de deux variables},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {157--219},
     publisher = {Gauthier-Villars},
     volume = {4e s{\'e}rie, 7},
     year = {1891},
     language = {fr},
     url = {http://archive.numdam.org/item/JMPA_1891_4_7__157_0/}
}