Delaunay normalisations

Too many terms are generated by a Delaunay normalisation when the perturbation is developed in powers of the eccentricity. Ways of bypassing the expansion are discussed. There are: (i) Brouwer's method of implicit variables; (ii) the preparation by canonical transformations; and (iii) the application of representation theory for Lie algebras. Illustrations of the techniques are drawn from the main problem of satellite theory and from the (1–1) resonance at the triangular equilibrium in the restricted problem of three bodies.