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Completely right injective semigroups that are unions of groups†

Published online by Cambridge University Press:  18 May 2009

E. H. Feller
Affiliation:
University of Wisconsin, Milwaukee, U.S.A.
R. L. Gantos
Affiliation:
University of Wisconsin, Milwaukee, U.S.A.
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A semigroup S with 0 and 1 is termed completely right injective provided every right unitary S-system is injective. A necessary condition for a semigroup to be com-pletely right injective is given in [2]; namely, every right ideal is generated by an idempotent. An example in section 3 of this paper shows the existence of semigroups with 0 and 1 satisfying this condition which are not completely right injective. In [3], it is shown that the condition that every right and left ideal is generated by an idempotent is necessary and sufficient in the case that S is both completely right and left injective (called completely injective). Such a semigroup is an inverse semigroup with 0 whose idempotents are dually well-ordered.

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Research Article
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Copyright © Glasgow Mathematical Journal Trust 1971