Uwano, Yoshio From the Birkhoff-Gustavson normalization to the Bertrand-Darboux integrability condition. (English) Zbl 0965.70027 J. Phys. A, Math. Gen. 33, No. 37, 6635-6653 (2000). MSC: 70H09 70K60 PDFBibTeX XMLCite \textit{Y. Uwano}, J. Phys. A, Math. Gen. 33, No. 37, 6635--6653 (2000; Zbl 0965.70027) Full Text: DOI arXiv
Taşeli, H.; Eid, R. Converging bounds for the eigenvalues of multiminima potentials in two-dimensional space. (English) Zbl 0902.35078 J. Phys. A, Math. Gen. 29, No. 21, 6967-6982 (1996). MSC: 35P15 35J10 PDFBibTeX XMLCite \textit{H. Taşeli} and \textit{R. Eid}, J. Phys. A, Math. Gen. 29, No. 21, 6967--6982 (1996; Zbl 0902.35078) Full Text: DOI Link