[1] E. Hewitt, H. S. Zuckermann: The L1-algebra of a Commutative Semigroup. Trans. Amer. Math. Soc. 83 (1956) 70-97. MR 0081908

[2] M. Petrich: On the Structure of a Class of Commutative Semigroups. Czechoslovak Math. J. 14 (1964) 147-153. MR 0166284 | Zbl 0143.03403

[3] M. Sasaki: On the Isomorphism Problem of Certain Semigroups Constructed from Indexed Groups. Proceedings of the Japan Academy, Vol. 41, No. 9 (1965) 763-765. DOI 10.3792/pja/1195522240 | MR 0197604 | Zbl 0145.02203

[4] T. Tamura: Commutative Nonpotent Archimedian Semigroup with Cancellation Law I. Journal of the Gakugei, Tokushima University, Vol. VII (1957) 6-11, MR 0096741