@article{SM_1979_35_2_a1,
     author = {G. N. Kobzev},
     title = {On~$tt$-degrees of recursively enumerable {Turing} degrees},
     journal = {Sbornik. Mathematics},
     pages = {173--180},
     year = {1979},
     volume = {35},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1979_35_2_a1/}
}