@article{JMPA_1889_4_5__361_0,
     author = {Appell, P.},
     title = {Sur les invariants de quelques \'equations diff\'erentielles},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {361--423},
     publisher = {Gauthier-Villars},
     volume = {4e s{\'e}rie, 5},
     year = {1889},
     language = {fr},
     url = {http://www.numdam.org/item/JMPA_1889_4_5__361_0/}
}