A note on uniqueness of the normal form for quasi-integrable systems
The paper provides a proof of the fact that at non-resonant actions the normal form for a quasi-integrable Hamiltonian system, as defined by von Zeipel-Poincaré and Lie perturbation algorithms is unique. The proof is based upon analyticity and therefore it overcomes some algebraic difficulties.
scientific article; zbMATH DE number 148337