[1] Jürgensen H.: Inf-Halbverbände als syntaktische Halbgruppen. Acta Math. Acad. Sci. Hung. 31 (1978), 37-41. MR 0489043

[2] Jürgensen H.: Syntaktische Halbgruppen. Proc., 1st workshop-meeting on categoгical and algebraic methods in computer science and system theory, Herdecke, 1976. Bericht 37, Abteilung Informatik, Universität Dortmund.

[3] Lallement G., und E. Milito: Recognizable languages and finite semilattices of groups. Semigroup Forum 11 (1975), 181-184. MR 0388867

[4] Maxson C. J., und M. Zeller: Elementary $\Gamma$-languages and finite semilattices of groups. Semigroup Forum 13 (1976/77), 385-386 MR 0434004

[5] Milito E.: Persönliche Mitteilung. Zbl 0952.03065

[6] Zapletal J.: Distinguishing subsets of semilattices. Arch. Math. (Brno) 9 (1973), 73-83. MR 0364513

[7] Zapletal J.: On the characterization of semilattices satisfying the descending chain condition and some remarks on distinguishing subsets. Arch. Math. (Brno) 10 (1974), 123-128. MR 0379720