ABSTRACT
The theory of stability of the motion of systems with a finite number of degrees of freedom which was created by A.M. Lyapunov [1935] rests upon the three basic concepts:
(1) deviations of the perturbed motion from the nominal one must be infinitely small;
(2) during the motion there are no perturbing forces, i.e., in the equations of motion all factors of external or internal perturbations should be taken into account;
(3) the functioning interval of the system is unlimited.
