This chapter contains basic first properties of commutative semigroups: idempotents, subsemigroups, homomorphisms and congruences, ideals, ideal extensions, ℋ-classes and Schützenberger groups, free commutative semigroups, presentations. It is written for readers who are not familiar with semigroups and can therefore expect a few surprises.
KeywordsMaximal Subgroup Identity Element Zero Element Commutative Semigroup Positive Power
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