참고문헌
- A. Cima, F. Manosas, and J. Villadelprat, Isochronicity for Several Classes of Hamilton- ian Systems, J. Differential Equations 157 (1999), no. 2, 373-413 https://doi.org/10.1006/jdeq.1999.3635
- H. Ito, Convergence of Birkhoff Normal Forms for Integrable Systems, Comment. Math. Helv. 64 (1989), no. 3, 412-461 https://doi.org/10.1007/BF02564686
- J. Villadelprat, Index of Vector Fields on Manifolds and Isochronicity for Planar Hamiltonian Differential Systems, Ph. D. Thesis, Pub. Univ. Autonoma de Barcelona, 1999