1. Some questions of phrase structure grammars;Abraham;Computational Linguistics,1965
2. Die Konstruktionskomplexität context-freier Sprachen;Cremers,1972
3. Some restrictive devices for context-free grammars;Mayer;Information and Control,1972
4. Programmed grammars and classes of formal languages;Rosenkrantz;J. Assoc. Comput. Mach.,1969
5. Periodically time-variant context-free grammars;Salomaa;Information and Control,1970