@article{AL_1990_29_2_a7,
     author = {V. L. Selivanov},
     title = {Index sets of classes of hyperhypersimple sets},
     journal = {Algebra i logika},
     pages = {220--240},
     publisher = {mathdoc},
     volume = {29},
     number = {2},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1990_29_2_a7/}
}