1. Some Problems in the Theory of Non-linear Oscillations;Malkin,1956
2. First integrals and families of symmetric periodic motions of a reversible mechanical system;Tkhai;Prikl Mat Mekh,2006
3. The period in a family of non-linear oscillations and periodic motions of a possible system at a critical point of the family;Tkhai;Prikl Mat Mekh,2010
4. Rotational motions of mechanical systems;Tkhai;Prikl Mat Mekh,1999