@article{AL_1978_17_3_a3,
     author = {A. N. Degtev},
     title = {Three theorems on $tt$-degrees},
     journal = {Algebra i logika},
     pages = {270--281},
     publisher = {mathdoc},
     volume = {17},
     number = {3},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1978_17_3_a3/}
}