Operations Which Preserve Definability in Languages
Journal of the ACM (JACM)
Derivatives of Regular Expressions
Journal of the ACM (JACM)
The Mathematical Theory of Context-Free Languages
The Mathematical Theory of Context-Free Languages
FOCS '61 Proceedings of the 2nd Annual Symposium on Switching Circuit Theory and Logical Design (SWCT 1961)
Hi-index | 0.00 |
Each set of operations selected from union, intersection, complement, star, quotients, derivatives, word-reversal, and homomorphisms is investigated with respect to its closure of an arbitrary family of word-sets, as well as to its closure of an arbitrary family of regular languages. Certain sets are shown to produce a finite closure for every finite family of word-sets; others, to produce a finite closure only for every finite family of regular languages; in either case, the closure for a given family of regular languages can be calculated by algorithm. For a third class-of sets, the closure is not necessarily finite even for finite families of regular languages.