@article{MAN_1937__114_159944,
     author = {O.H. Keller},
     title = {\"Uber eine {Kovariante} bei {Cremona-Transformationen}},
     journal = {Mathematische Annalen},
     pages = {700--741},
     year = {1937},
     volume = {114},
     language = {de},
     url = {http://geodesic.mathdoc.fr/item/MAN_1937__114_159944/}
}