@article{AL_1979_18_4_a6,
     author = {V. L. Selivanov},
     title = {The structure of degrees of unsolvability of index sets},
     journal = {Algebra i logika},
     pages = {463--480},
     year = {1979},
     volume = {18},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1979_18_4_a6/}
}