Journal of the ACM (JACM)
Journal of the ACM (JACM)
Indexed Grammars—An Extension of Context-Free Grammars
Journal of the ACM (JACM)
Programmed Grammars and Classes of Formal Languages
Journal of the ACM (JACM)
The Boolean Closures of the Deterministic and Nondeterministic Context-Free Languages
Gesellschaft für Informatik e.V., 3. Jahrestagung
Formal languages and their relation to automata
Formal languages and their relation to automata
Computations with a restricted number of nondeterministic steps (Extended Abstract)
STOC '77 Proceedings of the ninth annual ACM symposium on Theory of computing
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The so-called Chomsky hierarchy [5], consisting of regular, context-free, context-sensitive, and recursively enumerable languages, does not account for many “real world” classes of languages, e.g., programming languages and natural languages [4]. This is one of the reasons why many attempts have been made to “refine” the original Chomsky classification. The main goal has been to describe languages which, for instance, are not context-free but are still context-sensitive, without using the powerful and complex concept of context-sensitive grammars.