@article{AL_1971_10_3_a3,
     author = {S. Kallibekov},
     title = {Index sets of degrees of unsolvability},
     journal = {Algebra i logika},
     pages = {316--326},
     publisher = {mathdoc},
     volume = {10},
     number = {3},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1971_10_3_a3/}
}