1. Proof of a theorem of A.N. Kolmogorov on the preservation of conditionally periodic motions under a small perturbation of the Hamiltonian;Arnolʼd;Uspekhi Mat. Nauk USSR,1963
2. A classical approach to the analyticity problem of center manifolds;Aulbach;J. Appl. Math. Phys. (ZAMP),1985
3. Invariant tori for non-conservative perturbations of integrable systems;Bambusi;NoDEA Nonlinear Differential Equations Appl.,2001
4. Differential-Difference Equations;Bellman,1963
5. Methods of Accelerated Convergence in Nonlinear Mechanics;Bogoljubov,1976