@article{AL_1974_13_1_a0,
     author = {S. D. Denisov},
     title = {Three theorems on elementary theories and $tt$-reducibility},
     journal = {Algebra i logika},
     pages = {5--8},
     publisher = {mathdoc},
     volume = {13},
     number = {1},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AL_1974_13_1_a0/}
}