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A semigroup is a set $S$ together with a binary operation that is associative. Examples of semigroups are the set of finite strings over a fixed alphabet (under concatenation) and the positive integers (under addition, maximum, or minimum). A monoid is a semigroup with a neutral element. Of course, any group is also a monoid/semigroup.

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Cancellation property for commutative monoid

Let $(M,+,e)$ be a commutative monoid with unit $e$. An element $a\in M$ is called cancellative element if for any $b,c \in M$ such that $a+b=a+c$ implies that $b=c$. Let $(\mathbf{N},+,0)$ the commut …
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