@article{MZM_1992_51_2_a2,
     author = {S. V. Bolotin},
     title = {Integrable billiards on surfaces of constant curvature},
     journal = {Matemati\v{c}eskie zametki},
     pages = {20--28},
     publisher = {mathdoc},
     volume = {51},
     number = {2},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1992_51_2_a2/}
}