1. H. Lamb, Hydrodynamics, 6th ed. (Cambridge U.P., London, 1932).
2. These are the only two instances of quadratic resonance among the lower order modes.
3. A. H. Nayfeh and D. T. Mook, Nonlinear Oscillations (Wiley, New York, 1979).
4. D. J. Benney, J. Fluid Mech. 14, 577 (1962).JFLSA70022-1120
5. L. F. McGoldrick, J. Fluid Mech. 21, 305 (1965).JFLSA70022-1120