@article{MZM_1994_55_5_a2,
     author = {Ya. B. Vorobets},
     title = {On the measure of the set of periodic points of the billiard},
     journal = {Matemati\v{c}eskie zametki},
     pages = {25--35},
     publisher = {mathdoc},
     volume = {55},
     number = {5},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1994_55_5_a2/}
}