1. The reversibility of mechanical systems;Tkhai;Prikl. Mat. Mekh.,1991
2. Periodic solutions for differential systems with symmetries;Heinbockel;J. Soc. Indust. Appl. Math.,1965
3. Hopf bifurcation in the problem of the motion of a heavy rigid body on a rough surface;Karapetyan;Izv. Akad. Nauk. SSSR, MTT,1985
4. Dynamics of a Body in Contact with a Rigid Surface;Markeyev,1992
5. Local Method for the Non-linear Analysis of Differential Equations;Bryuno,1979