Context-free languages and pushdown automata
Handbook of formal languages, vol. 1
Set constraints in some equational theories
Information and Computation
Two Families of Languages Related to ALGOL
Journal of the ACM (JACM)
Conjunctive Grammars and Systems of Language Equations
Programming and Computing Software
Valid identity problem for shuffle regular expressions
Journal of Automata, Languages and Combinatorics
Unification in a Description Logic with Transitive Closure of Roles
LPAR '01 Proceedings of the Artificial Intelligence on Logic for Programming
The Complexity of Set Constraints
CSL '93 Selected Papers from the 7th Workshop on Computer Science Logic
Information and Computation
On binary ⊕-NFAs and succinct descriptions of regular languages
Theoretical Computer Science - Implementation and application of automata
Theoretical Computer Science - Mathematical foundations of computer science 2004
Unresolved systems of language equations: expressive power and decision problems
Theoretical Computer Science
Reversal-bounded multipushdown machines
Journal of Computer and System Sciences
Decision problems for language equations with Boolean operations
ICALP'03 Proceedings of the 30th international conference on Automata, languages and programming
Strict language inequalities and their decision problems
MFCS'05 Proceedings of the 30th international conference on Mathematical Foundations of Computer Science
The power of commuting with finite sets of words
STACS'05 Proceedings of the 22nd annual conference on Theoretical Aspects of Computer Science
What do we know about language equations?
DLT'07 Proceedings of the 11th international conference on Developments in language theory
Language equations with complementation: Expressive power
Theoretical Computer Science
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Systems of language equations used by Ginsburg and Rice (“Two families of languages related to ALGOL”, JACM, 1962) to represent context-free grammars are modified to use the symmetric difference operation instead of union. Contrary to a natural expectation that these two types of equations should have incomparable expressive power, it is shown that equations with symmetric difference can express every recursive set by their unique solutions, every recursively enumerable set by their least solutions and every co-recursively-enumerable set by their greatest solutions. The solution existence problem is Π1-complete, the existence of a unique, a least or a greatest solution is Π2-complete, while the existence of finitely many solutions is Σ3-complete.