1. Sur certaines vibrations d'ordre supérieur et d'intensité anomale, vibrations dans les mécanismes à plusiers degrés de liberté;Korteweg;Arch. Nederl. Sci. Exactes et Natur.,1898
2. The oscillations about a position of equilibrium where a simple linear relation exists between the frequencies of the principal vibrations;Beth;Phil. Mag.,1913
3. Oscillations of an elastic pendulum as an example of oscillations of two parametrically coupled linear systems;Vitt;Zh. Tekh. Fiz.,1933
4. Nonlinear resonances affecting gravity gradient stability;Breakwell,1965
5. The Motion of an Artificial Satellite Relative to its Centre of Mass in a Gravitational Field;Beletskii,1975