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2. T. B. Enginol, Boğaziçi University Publication, 36/001, (1975); for a summary in English, see also Boğaziçi Univ. J., 3:187, (1975).
3. N. N. Bogoljubov and J. A. Mitropolski, “Asymptotische Methoden in der Nichtlinearen Schwinggungen”, Akademie Verlag (1965).
4. M. Urabe, “Nonlinear Autonomous Oscillations”, Academic Press, (1967).
5. T. B. Enginol, On The Asymptotic Stability of Nuclear Reactors with Arbitrary Feedback, Nucl. Sci. Eng., 90:231 (1985).