ON THE POWER OF COOPERATING MORPHISMS VIA REACHABILITY PROBLEMS

Abstract

The goal of this presentation is to analyze the equality mechanism of cooperating morphisms of free monoids, and to point out how it can be used to define the reachability problems leading to important undecidability results and easy characterizations of recursively enumerable languages. In particular, we aim to show, which subconstructions are needed in such results. Moreover, we recall that in some cases the undecidability of the reachability is achieved although the sets of all reachable objects are simple, or more formally, regular languages.