1. Atherton DP (1975) Nonlinear control engineering. Van Nostrand Reinhold, London, Full edition 1975, student edition 1982
2. Bendat JS (1990) Nonlinear system analysis and identification from random data. Wiley, New York, NY
3. Billings SA, Lang ZQ (1996) A bound of the magnitude characteristics of nonlinear output frequency response functions. Int J Control, Part 1, 65(2):309–328 and Part 2, 65(3):365–384
4. Billings SA, Lang ZQ (2002) Nonlinear systems in the frequency domain: energy transfer filters. Int J Control 75(14):1066–1081
5. Billings SA, Peyton-Jones JC (1990) Mapping nonlinear integro-differential equation into the frequency domain. Int J Control 54:863–879