@article{VMUMM_1991_1_a13,
     author = {I. I. Chigur},
     title = {Branching billiards},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {68--72},
     publisher = {mathdoc},
     number = {1},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1991_1_a13/}
}