- I K Kozlov, “The topology of the Liouville foliation for the Kovalevskaya integrable case on the Lie algebra so(4)”, Sb. Math., 205, № 4, 2014,
532 
- E. A. Kudryavtseva, A. A. Oshemkov, “Structurally Stable Nondegenerate Singularities of Integrable Systems”, Russ. J. Math. Phys., 29, № 1, 2022,
57