@article{DAN_1979_245_2_a1,
     author = {G. A. Gal'perin},
     title = {On systems of perfectly elastic balls moving in space or in a box},
     journal = {Doklady Akademii Nauk},
     pages = {285--288},
     publisher = {mathdoc},
     volume = {245},
     number = {2},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1979_245_2_a1/}
}