Finite automata and unary languages
Theoretical Computer Science
Unrestricted complementation in language equations over a one-letter alphabet
Theoretical Computer Science
Two Families of Languages Related to ALGOL
Journal of the ACM (JACM)
Journal of Automata, Languages and Combinatorics - Special issue: selected papers of the second internaional workshop on Descriptional Complexity of Automata, Grammars and Related Structures (London, Ontario, Canada, July 27-29, 2000)
Conjunctive Grammars and Systems of Language Equations
Programming and Computing Software
Simulating finite automata with context-free grammars
Information Processing Letters
Language equations with complementation
DLT'06 Proceedings of the 10th international conference on Developments in Language Theory
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It has recently been proved (Jeż, DLT 2007) that conjunctive grammars (that is, context-free grammars augmented by conjunction) generate some nonregular languages over a one-letter alphabet. The present paper improves this result by constructing conjunctive grammars for a larger class of unary languages. The results imply undecidability of a number of decision problems of unary conjunctive grammars, as well as nonexistence of an r.e. bound on the growth rate of generated languages. An essential step of the argument is a simulation of a cellular automaton recognizing positional notation of numbers using language equations.