1. Teschl Gerald (2011) Ordinary differential equations and dynamical systems. American Mathematical Society, Providence, Rhode Island
2. Stoker JJ (1950) Nonlinear vibrations. Interscience Publishers, New York
3. Wang HQ (1992) Nonlinear vibrations. Higher Education Press, Beijing
4. Van der Pol B (1920) A theory of the amplitude of free and forced triode vibrations. Radio Review, 1: 701–710, 754–762
5. Van der Pol B (1927) Forced oscillations in a circuit with non-linear resistance (reception with reactive triode). The London, Edinburgh, and Dublin Philos Mag J Sci Ser 7, 3:65–80