Let S be a commutative
semigroup. The main theorem in this paper is to prove that the following two
conditions are equivalent: (1) For all a,b ∈ S there are positive integers m,n such
that am = bn. (2) For all a,b ∈ S,al = ambn,bγ = bsat for some l,m,n,r,s,t. As a
consequence of the theorem, the authors prove that a commutative archimedean
semigroup S without idempotent is power joined if and only if the structure group of
S is a torsion group.
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