from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Any subset of a semigroup that is closed under the semigroup operation.
The semigroup of all nonempty words over a given alphabet has as a subsemigroup the words of even length; however the words of odd length do not form a subsemigroup because the concatenation of two odd-length words is not of odd length.
A monoid H is a submonoid of a monoid G when it is a subsemigroup of G that includes the identity of G. 2.2 Groups
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