Abstract
AbstractCourcelle introduced the study of regular words, i.e., words isomorphic to frontiers of regular trees. Heilbrunner showed that a nonempty word is regular iff it can be generated from the singletons by the operations of concatenation, omega power, omega-op power, and the infinite family of shuffle operations. We prove that the nonempty regular words, equipped with these operations, are the free algebras in a variety which is axiomatizable by an infinite collection of some natural equations.
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