[1] J. L. Chrislock: The structure of archimedean semigroups. thesis, Univ. of Calif., Davis. 1966.

[2] J. L. Chrislock: On medial semigroups. J. Algebra 12 (1969), 1 - 9. DOI 10.1016/0021-8693(69)90013-1 | MR 0237685 | Zbl 0187.29102

[3] A. H. Clifford, G. B. Preston: The algebraic theory of semigroups. Vol. 1, Survey 7, Amer. Math. Soc., Providence, R. I., 1961. MR 0132791 | Zbl 0111.03403

[4] J. С. Higgins: Finitely generated commutative archimedean semigroups without idempotent. thesis, Univ. of Calif., Davis, 1966.

[5] J. С. Higgins: Representing N-semigroups. Bull. Australian Math. Soc., Vol. 1, 1969, 115-126. DOI 10.1017/S0004972700041320 | MR 0248252 | Zbl 0169.33302

[6] R. Levin, T. Tamura: On locally cyclic semigroups. Proc. Japan Acad. 42, 4 (1966), 376-379. MR 0204561 | Zbl 0166.27701

[7] M. Petrich: On the structure of a class of commutative semigroups. Czech. Math. J. 14 (1964), 147-152. MR 0166284 | Zbl 0143.03403

[8] L. Rédei: The theory of finitely generated commutative semigroups. Pergamon Press, 1965. MR 0188322

[9] T. Tamura: Commutative nonpotent archimedean semigroups with cancellation law 1. Journ. of Gakugei, Tokushima Univ., 8 (1957), 5-11. MR 0096741

[10] T. Tamura: Abelian groups and $\Re$-semigroups. Proc. Japan Acad., 46 (1970), 212-216. MR 0274618