Some Restrictive Devices for Context-Free Grammars

For context-free grammars the restrictive devices of unordered scattered context, random context, partial ordering of productions and concatenation of productions in matrices are compared with respect to their generative power. This leads to two new characterizations of the family of type O languages in terms of unordered scattered context grammars and random context grammars, respectively. Languages generated by context-free grammars by imposing one of the above-mentioned restrictive devices or programming, regular control language, periodic time-variance or context-sensitivity are shown to have in the case of finite index a property similar to the “uvwxyproperty≓ of context-free languages.