Georgieva, B., and R. B. Guenther. “First Noether-Type Theorem for the Generalized Variational Principle of Herglotz”. Topological Methods in Nonlinear Analysis, vol. 20, no. 2, Dec. 2002, pp. 261-73, https://apcz.umk.pl/TMNA/article/view/TMNA.2002.036.