“SYMMETRIES OF THE HERGLOTZ VARIATIONAL PRINCIPLE IN THE CASE OF ONE INDEPENDENT VARIABLE” (2011) Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, 100, pp. 113–122. Available at: https://annual.uni-sofia.bg/index.php/fmi/article/view/249 (Accessed: 14 December 2025).