@article{JOLT_2001_11_2_a6,
     author = {W. Bertram and J. Hilgert},
     title = {Characterization of the {Kantor-Koecher-Tits} {Algebra} by a {Generalized} {Ahlfors} {Operator}},
     journal = {Journal of Lie Theory},
     pages = {415--426},
     year = {2001},
     volume = {11},
     number = {2},
     zbl = {1049.53037},
     url = {http://geodesic.mathdoc.fr/item/JOLT_2001_11_2_a6/}
}