@article{MZ_1990__205_3_174198,
     author = {J.-P. Tignol and M. Denert and Jan Van Geel},
     title = {The level of cyclic division algebras.},
     journal = {Mathematische Zeitschrift},
     pages = {603--616},
     publisher = {mathdoc},
     volume = {205},
     number = {3},
     year = {1990},
     zbl = {0724.12004},
     url = {http://geodesic.mathdoc.fr/item/MZ_1990__205_3_174198/}
}