@article{ZNSL_2005_325_a6,
     author = {F. S. Duzhin},
     title = {Lower bounds on the number of closed trajectories of generalized billiards},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {113--126},
     publisher = {mathdoc},
     volume = {325},
     year = {2005},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2005_325_a6/}
}