1. The Hamiltonian Hopf Bifurcation;van der Meer,1985
2. Unique normal forms: the nilpotent Hamiltonian case;Baider;J. Diff. Eqns.,1991
3. Dynamical Systems;Birkhoff,1927
4. Proof of a generalized form of a fixed point theorem due to G.D. Birkhoff;Moser,1977