@article{VMUMM_2021_4_a8,
     author = {V. V. Vedyushkina},
     title = {Orbital invariants of flat billiards bounded by arcs of confocal quadrics and containing focuses},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {48--51},
     publisher = {mathdoc},
     number = {4},
     year = {2021},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_2021_4_a8/}
}