1. W. Brauer, On grammatical complexity of context-free languages (extended abstract). in: {itProc. of MFCS'73}, 191–196.
2. A connection between descriptional complexity of context-free grammars and grammar form theory;Csuhaj-Varjú,1987
3. On bounded interpretations of grammar forms;Csuhaj-Varjú;Theoret. Comput. Sci.,1991
4. On a classification of context-free grammars;Gruska;Kybernetika,1967
5. Some classifications of context-free languages;Gruska;Inform. and Control,1969