Commutative Semigroups


Definition

A commutative semigroup is a semigroup

Basic Results

Examples

Representation

Decision problems

Equational Theory: Decidable
Quasi-equational Theory: Decidable
First order theory: Undecidable

Spectra and growth

Finite spectrum:
Free spectrum: 1,

Subvarieties

countably many, including semilattices, constant semigroups

Expansions

commutative monoids