Publication at Faculty of Mathematics and Physics |
2013
Abstract
A concrete category is almost universal if its class of non-constant morphisms contains an isomorphic copy of every category of algebras as a full subcategory. This paper characterizes almost universal varieties of commutative semigroups.
As a consequence we obtain that for every infinite cardinal $\kappa$ there exists a commutative semigroup of cardinality $\kappa$ such that it has exactly two endomorphisms, the identity endomorphism and a single constant endomorphism.