Noneffective Regularity of Equality Languages and Bounded Delay Morphisms
Juhani Karhumäki, Aleksi Saarela · Discrete Mathematics & Theoretical Computer Science · 2010
special issue dedicated to the second edition of the conference AutoMathA: from Mathematics to Applications We give an instance of a class of morphisms for which it is easy to prove that their equality set is regular, but its emptiness is still undecidable. The class is that of bounded delay 2 morphisms.