Non-integrability of a Hamiltonian system, based on a problem of nonlinear vibration of an elastic string. Ann. Sofia Univ. Fac. Math. and Inf. [Internet]. 2009 Dec. 12 [cited 2025 Dec. 16];99:137-53. Available from: https://annual.uni-sofia.bg/index.php/fmi/article/view/118