@article{MAN_1882__19_156993,
     author = {Christoffel},
     title = {Bemerkungen zur {Invariantentheorie}},
     journal = {Mathematische Annalen},
     pages = {280--290},
     year = {1882},
     volume = {19},
     url = {http://geodesic.mathdoc.fr/item/MAN_1882__19_156993/}
}