Theory of recursive functions and effective computability
Theory of recursive functions and effective computability
Degrees of Unsolvability in Formal Grammars
Journal of the ACM (JACM)
General Problems of Formal Grammars
Journal of the ACM (JACM)
Bounded context syntactic analysis
Communications of the ACM
Formal languages and their relation to automata
Formal languages and their relation to automata
Enumeration of context-free languages and related structures
Journal of Automata, Languages and Combinatorics
The use of lists in the study of undecidable problemsin automata theory
Journal of Computer and System Sciences
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After a brief discussion of historical matters in §1, twenty-seven predicates of formal grammers are introduced in §2. The next two sections discuss recursively enumerable predicates and nonrecursively enumerable predicates, respectively. These results show that the degree of unsolvability of a predicate is determined by its domain of definition. The paper concludes with a degree diagram and suggestions for further development. From a more comprehensive point of view these results complement the computational complexity classification of solvable problems and extend that classification to unsolvable problems based on their degree of unsolvability.