@article{JRAM_1868__68_148041,
     author = {E.B. Christoffel},
     title = {Theorie der bilinearen {Functionen.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {253--272},
     publisher = {mathdoc},
     volume = {68},
     year = {1868},
     language = {de},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1868__68_148041/}
}