1. Ford, J.: The Fermi-Pasta-Ulam problem: paradox turns discovery. Phys. Rep. 213(5), 271–310 (1992)
2. Siegel, C.I.: On the integrals of canonical systems. Ann. Math. 42, 806–822 (1941)
3. Fermi, E., Pasta, J., Ulam, S.: Studies in nonlinear problems, I.
Los Alamos Report LA-1940, (1955). Article is reproduced in:
Newell, A.C., (ed.) Nonlinear Wave Motion, Am. Mathematical Soc.,
(1974) and in: Tabor, M.: Chaos and Integrability in Nonlinear
Dynamics: An Introduction, The FUP Experiment p. 280. John Wiley
and Sons, New York (1989)