1. Andronov, A A, Vitt, A A and Khaikin, S E. 1987.Theory of oscillators, 340–350. 585–613. Dover: Dover Publications.
2. Bogoliubov, N N and Mitropolsky, Y A. 1961.Asymptotic methods in the theory of non linear oscillations, 80–91. New York: Gordon & Breach.
3. (Too Many) Mathematical Models of Circadian Clocks (?)