@article{JLT_1991_1_1_a5,
     author = {U. Zimmermann},
     title = {Invariante {Kegel} in {Cartan-Algebren}},
     journal = {Journal of Lie theory},
     pages = {055--064},
     publisher = {mathdoc},
     volume = {1},
     number = {1},
     year = {1991},
     url = {http://geodesic.mathdoc.fr/item/JLT_1991_1_1_a5/}
}