1. Clifford, A. and G. Preston,The algebraic theory of semigroups, 1964.
2. Hoehnke, H. J.,Structure of semigroups, Canad. J. Math.32 (1966), 449–491.
3. Kelarev, A. V.,Radicals and bands of semigroups, Isv. vysh. uch. sav., Matematika (1988), 81–83 (in Russian).
4. Kelarev, A. V.,Hereditary radicals and 0-bands of semigroups, Semigroup Forum38 (1989), 57–76.
5. Kelarev, A. V.,Radicals and bands of associative rings, Algebra i logika (Novosibirsk)28 (1989), 430–441 (in Russian).