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- [37] COMMUTATIVE SEMIGROUP AND POWER JOINED SUBSEMIGROUPS NOTICES OF THE AMERICAN MATHEMATICAL SOCIETY, 1969, 16 (03): : 555 - &
- [38] NILPOTENT ELEMENTS OF COMMUTATIVE SEMIGROUP RINGS NOTICES OF THE AMERICAN MATHEMATICAL SOCIETY, 1974, 21 (07): : A604 - A604