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A totally ordered monoid - or tomonoid, for short - is a commutative semigroup with identity S equipped with a total order ≤s that is translation invariant, i.e., that satisfies: ∀x, y, z ∈, x ≤s y ⇒ x + z ≤s y + z. We call a tomonoid that is a quotient of some totally ordered free commutative monoid formally integral. Our most significant results concern characterizations of this condition by means of constructions in the lattice Zn that are reminiscent of the geometric interpretation of the Buchberger algorithm that occurs in integer programming. In particular, we show that every two-generator tomonoid is formally integral. In addition, we give several (new) examples of tomonoids that are not formally integral, we present results on the structure of nil tomonoids and we show how a valuation-theoretic construction due to Hion reveals relationships between formally integral tomonoids and ordered commutative rings satisfying a condition introduced by Henriksen and Isbell.

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Semigroup Forum

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