1. On a classification of context-free languages;Gruska;Kybernetika,1967
2. Complexity and minimality of context-free grammars and languages;Cerný,1977
3. Some classifications of context-free languages;Gruska;Inf. Control,1969
4. Complexity and unambiguity of context-free grammars and languages;Gruska;Inf. Control,1971
5. On the size of context-free grammars;Gruska;Kybernetika,1972