@article{JMPA_1930_9_9__327_0,
     author = {Hazlett, Olive C.},
     title = {On formal modular invariants},
     journal = {Journal de Math\'ematiques Pures et Appliqu\'ees},
     pages = {327--332},
     publisher = {Gauthier-Villars},
     volume = {Ser. 9, 9},
     year = {1930},
     language = {en},
     url = {http://archive.numdam.org/item/JMPA_1930_9_9__327_0/}
}