“…is a semigroup because it is closed under .. Since R is finite, so is S. For each r in S, there is a positive integer n depending on r such that r n = r, so r n-1 is the identity of r. Moreover, since r is a left nonzerodivisor, r n-1 is the unique right identity of r. Noting that r n-1 is an idempotent, we have /~----rn-l.R ~-R' such that rn-lR'~-O, and hence R'-~O for r n-1 is in S (see the proof of Lemma 1.2 in [6]). Thus the idempotent r "-1 is a left identity of R. From what has been done, it is easy to show that S is a partition of the subgroups Se~, where {el,e2,...,en; for some integer n}are all different nonzero idcmpotents of/~ such that S e~ ~-S e I by I,l (s e~)----~-se~ej-~se~ for each s in S and i,j-----1,2 ..... n (see the proof of Th.…”