@article{VMUMM_1990_4_a5,
     author = {Sh. Sh. Kary-Niyazov},
     title = {Classes of co-absoluteness of {Borel} and {hyper-Borel} sets},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {21--26},
     publisher = {mathdoc},
     number = {4},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1990_4_a5/}
}