On Decompositions of Regular Events
Journal of the ACM (JACM)
Complexity measures for regular expressions
STOC '74 Proceedings of the sixth annual ACM symposium on Theory of computing
The limitedness problem on distance automata: Hashiguchi's method revisited
Theoretical Computer Science
On Concatenative Decompositions of Regular Events
IEEE Transactions on Computers
Complexity in union-free regular languages
DLT'10 Proceedings of the 14th international conference on Developments in language theory
On union-free and deterministic union-free languages
TCS'12 Proceedings of the 7th IFIP TC 1/WG 202 international conference on Theoretical Computer Science
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A regular language is called union-free if it can be represented by a regular expression that does not contain the union operation. Every regular language can be represented as a finite union of union-free languages (the so-called union-free decomposition ), but such decomposition is not necessarily unique. We call the number of components in the minimal union-free decomposition of a regular language the union width of the regular language. In this paper we prove that the union width of any regular language can be effectively computed and we present an algorithm for constructing a corresponding decomposition. We also study some properties of union-free languages and introduce a new algorithm for checking whether a regular language is union-free.