@article{BagderinaTarkhanov2014,
  author    = {Yulia Yu. Bagderina and Nikolai Nikolaevich Tarkhanov},
  title     = {Differential invariants of a class of Lagrangian systems with two degrees of freedom},
  journal   = {Journal of mathematical analysis and applications},
  volume    = {410},
  number    = {2},
  pages     = {733 -- 749},
  doi       = {10.1016/j.jmaa.2013.08.015},
  year      = {2014},
}