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 II1-complete, the existence of a unique, a least or a greatest solution is ∏2-complete, while the existence of finitely many solutions is Σ3-complete.
| Original language | English |
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| Title of host publication | Computer Science - Theory and Applications, First International Computer Science Symposium in Russia, CSR 2006, St. Petersburg, Russia, June 8-12, 2006, Proceedings |
| Editors | Dima Grigoriev, John Harrison, Edward A. Hirsch |
| Pages | 292-303 |
| Number of pages | 12 |
| Volume | 3967 LNCS |
| DOIs | |
| State | Published - 2006 |
| Externally published | Yes |
| Event | 1st International Computer Science Symposium in Russia, CSR 2006 - St. Petersburg, Russian Federation Duration: 8 Jun 2006 → 12 Jun 2006 |
| Name | Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) |
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| Publisher | Springer Nature |
| ISSN (Print) | 0302-9743 |
| Conference | 1st International Computer Science Symposium in Russia, CSR 2006 |
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| Country/Territory | Russian Federation |
| City | St. Petersburg |
| Period | 8/06/06 → 12/06/06 |
ID: 78926614