@unpublished{BagderinaTarkhanov2013,
  author  = {Yulia Yu. Bagderina and Nikolai Nikolaevich Tarkhanov},
  title   = {Differential invariants of a class of Lagrangian systems with two degrees of freedom},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprints des Instituts f{\"u}r Mathematik der Universit{\"a}t Potsdam},
  number    = {2 (2013) 2},
  year    = {2013},
}