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@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/} }
Ya. B. Vorobets. On the measure of the set of periodic points of the billiard. Matematičeskie zametki, Tome 55 (1994) no. 5, pp. 25-35. http://geodesic.mathdoc.fr/item/MZM_1994_55_5_a2/