1. A Survey of the Theory of the Boundedness, Stability, and Asymptotic Behavior of Solutions of Linear and Nonlinear Differential and Difference Equations;Bellman;Office of Naval Research Report NAVEXOS,1949
2. Forced Oscillations in Nearly Sinusoidal Systems,;Cartwright;J. Inst. Elec. Engrs.,1948
3. On Nonlinear Differential Equations of the Second Order: III,;Cartwright;Proc. Cambridge Phil. Soc.,1949
4. Forced Oscillations in Nonlinear Systems;Cartwright,1950