Co-Regular Languages and Uni cation of Co-Regular Languages

The main goal of this work is the investigation of some properties of co-regular languages. In many applications it is important to handle innnite sets of terms. We represent two equivalent formalisms for nite deened innnite sets of term substitutions which are leading to co-regular languages. As it will be proved later the co-regular languages are monoidic homomorphical images of regular languages. A natural deenition of uniication of co-regular languages is introduced. This paper is a compressed version of Mi93]. 1 Monoids In this section we present a brief introduction in the monoid theory.