1. V. E. Zakharov, L. A. Takhtadzhyan, and L. D. Faddeev, “Complete description of solutions of the ‘sine-Gordon’ equation,” Soviet Phys. Dokl., 19, 824–826 (1974).
2. M. J. Ablowitz, D. J. Kaup, A. C. Newell, and H. Segur, “Method for solving the sine-Gordon equation,” Phys. Rev. Lett., 30, 1262–1264 (1973).
3. E. Bour, Théorie de la déformation des surfaces, Gauthier-Villars, Paris (1861).
4. A. V. Bäcklund, “Ueber flächentransformationen,” Math. Ann., 9, 297–320 (1875).
5. J. Frenkel and T. Kontorova, “Propagation of dislocation in crystals,” J. Phys. USSR, 1, 348 (1939).