1. On the structure of a class of commutative semigroups;Petrich;Czechoslovak Math. J.,1964
2. [1] Higgins John Clayborn , Finitely generated commutative archimedean semigroups with idempotent, doctoral dissertation, University of California at Davis, unpublished (1966).
3. On the base of the infinite quasipower semigroup;Tamura;Shikokie Shijo. Danwa,1963
4. On locally cyclic semigroups;Tamura;Proc. Japan Acad.,1966
5. The theory of operations on binary relations