1. Asymptotic Behavior and Stability Problems in Ordinary Differential Equations;Cesari,1963
2. Perturbation Methods in Applied Mathematics;Cole,1968
3. Asymptotic Methods in the Theory of Non-linear Oscillations;Bogoliubov,1961
4. Asymptotic methods in the theory of linear differential equations;Feshchenko;NASA TTF-458,1967
5. Perturbation Methods;Nayfeh,1973