Fixed Point Languages, Equality Languages, and Representation of Recursively Enumerable Languages

Abstract

Fixed point languages and equality languages of homomorphisms and dgsm mappings are considered. Some basic properties of these classes of languages are proved, and it is shown how to use them to represent recursively enumerable sets. In particular, very simple languages are introduced which play the same role for the class of recursively enumerable languages that the Dyck languages play for the class of context-free languages. Finally, a new type of acceptor for defining equality languages is introduced. © 1980, ACM. All rights reserved.