@article{VMUMM_1987_5_a15,
     author = {D. V. Treschev},
     title = {On the problem of the periodic trajectories of the {Birkhoff} billiard},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {72--75},
     year = {1987},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1987_5_a15/}
}