1. S. Adian. Definining relations and algorithmic problems for groups and semigroups. Trudy Matem. in-ta im. Steklova AN SSSR, 85, 1996 (Russian).
2. S. Adian. Transformations of words in a semigroup presented by a system of defining relations. Algebra i logika, 15(6),611–621, 1976 (Russian).
3. S. Adian, and G. Oganesian. On the word and divisibility problems in semigroups with a single defining relation. Izv. An. SSSR Ser. Matem., 42(2),219–225, 1978 (Russian).
4. J. Bouwsma. Semigroups Presented by a Single Relation. PhD dissertation at Pennsylvania State University, 1993.
5. C. Kirchner. Computing unification algorithms. In Proceedings of the First Symposium on Logic in Computer Science, Boston, 200–216, 1990.