1. Cunningham, W.J.: Introduction to nonlinear analysis, (McGraw-Hill, New York 1958), p. 157–168
2. Thompson, J.M.T., and Stewart, H.B.: Nonlinear dynamics and chaos, (Wiley, Chichester, UK 1989)
3. Moon, F.C.: Chaotic vibrations — an introduction for applied scientists and engineers, (Wiley, Chichester, UK 1987)