1. Asymptotic Methods in the Theory of Non-linear Oscillations;Bogolyubov,1974
2. Averaging Methods in the Theory of Non-linear Oscillatory Systems;Volosov,1971
3. Asymptotic Methods of Optimal Control;Akulenko,1987
4. Mathematical Theory of Optimal Processes;Pontryagin,1969
5. Passage across the separatrix in a resonant problem with slowly varying parameters;Neishtadt;Prikl. Mat. Mekh.,1975