@article{JMAG_2002_9_a8,
     author = {S. V. Naydenov and V. V. Yanovskii},
     title = {Normal forms of billiards},
     journal = {\v{Z}urnal matemati\v{c}eskoj fiziki, analiza, geometrii},
     pages = {663--685},
     publisher = {mathdoc},
     volume = {9},
     year = {2002},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/JMAG_2002_9_a8/}
}