@article{ND_2017_13_3_a9,
     author = {I. A. Bizyaev and A. V. Borisov and I. S. Mamaev},
     title = {The {Hess{\textendash}Appelrot} case and quantization of the rotation number},
     journal = {Russian journal of nonlinear dynamics},
     pages = {433--452},
     publisher = {mathdoc},
     volume = {13},
     number = {3},
     year = {2017},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ND_2017_13_3_a9/}
}