1. A. N. Degtev, "Ontt - andm - degrees," Algebra Logika,12, No. 2, 143–161 (1973).
2. A. N. Degtev, "On semilattices of disjunctive and linear degrees," Mat. Zametki,38, No. 2, 310–316 (1985).
3. A. N. Degtev and D. A. Zakharov, Denumberable Sets [in Russian], Novosibirsk State Univ., (1979), pp. 1–92.
4. S. D. Zakharov, "One - ands - degrees," Algebra Logika,23, No. 4, 395–406 (1984).
5. G. N. Kobzev, "Onftt - reducibility," Algebra Logika,12, No. 2, 190–204 (1973).