Positive First-order Logic on Words and Graphs
We study FO+, a fragment of first-order logic on finite words, where monadic predicates can only appear positively. We show that there is an FO-definable language that is monotone in monadic predicates but not definable in FO+. This provides a simple proof that Lyndon's preservation theorem fai...
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| Format: | Article |
| Language: | English |
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Logical Methods in Computer Science e.V.
2023-07-01
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| Series: | Logical Methods in Computer Science |
| Subjects: | |
| Online Access: | https://lmcs.episciences.org/9081/pdf |