1. Benson, D.: Syntax and Semantics: A Categorical View, Inf and Con (1970)
2. Bertsch, E.: Existenz-und Entscheidbarkeitsfragen der Ubersetzungstheorie, Doct.Thesis, Saarbrücken (1973)
3. id.: Mappings between Context-free Derivation Systems, Lecture Notes in Computer Science 2 (1973)
4. id.: Surjectivity of Functors on Grammars (submitted to a technical journal)
5. Brauer, W. and K. Indermark: Algorithmen, rekursive Funktionen und formale Sprachen, BI-HTB 817 (1968)