  We prove the necessary and sufficient conditions for practical stability of
nonlinear dynamical system at general phase restrictions. In such a case the
Lyapunov function is nondifferentiable. But if the set of initial data is
starry compact, then it is possible building Lyapunov function which belongs to
differentiable functions class. We also estimate the optimal sets of initial
conditions in structural forms for linear system and concrete phase
restrictions.
