Georgieva, Bogdana. “SYMMETRIES OF THE HERGLOTZ VARIATIONAL PRINCIPLE IN THE CASE OF ONE INDEPENDENT VARIABLE”. Ann. Sofia Univ. Fac. Math. and Inf. 100 (December 12, 2011): 113–122. Accessed November 25, 2024. https://annual.uni-sofia.bg/index.php/fmi/article/view/249.