%0 Journal Article %A A. V. Ostrovsky %T On a question of L. V. Keldysh concerning the structure of Borel sets %J Sbornik. Mathematics %D 1988 %P 317-337 %V 59 %N 2 %U http://geodesic.mathdoc.fr/item/SM_1988_59_2_a3/ %G en %F SM_1988_59_2_a3