@article{SEMR_2009_6_a26,
     author = {V. V. Ivanov},
     title = {Dynamic quadrangles and isochronous oscillations},
     journal = {Sibirskie \`elektronnye matemati\v{c}eskie izvesti\^a},
     pages = {381--384},
     publisher = {mathdoc},
     volume = {6},
     year = {2009},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/SEMR_2009_6_a26/}
}