On homomorphic images of szilard languages

In this paper we study homomorphic images of Szilard languages (of context-free grammars). First, the relationship between context-free languages and homomorphic images of Szilard languages is considered. Secondly, it is shown that there is a proper hierarchy of language classes. , is the class of languages obtained from Szilard languages by homomorphisms h such that the length of h(ρ) is at most i for each label ρ