1. A. H. Clifford and G. B. Preston, Algebraic Theory of Semigroups [Russian translation], Vols. 1, 2, Mir, Moscow (1972).
2. T. Tamura, “Commutative semigroups whose lattice of congruences is a chain,” Bull. Soc. Math. France, 97, 369–380 (1969).
3. B. M. Schein, “Commutative semigroups where congruences form a chain,” Bull. Acad. Pol. Sci., Sér. Sci. Math. Astron. Phys., 17, 523–527 (1969).
4. B. M. Schein, “Corrigenda to ‘Commutative semigroups where congruences form a chain,’” Bull. Acad. Pol. Sci., Sér. Sci. Math. Astron. Phys., 12, 1247 (1975).
5. H. Mitsch, “Semigroups and their lattice of congruences. I,” Semigroup Forum, 26, 1–63 (1983).