Positive and monotone fragments of FO and LTL
Résumé
We study the positive logic FO+ on finite words, and its fragments, pursuing and refining the work initiated in [Kuperberg 2023]. First, we transpose notorious logic equivalences into positive first-order logic: FO+ is equivalent to LTL+ , and its two-variable fragment FO2+ with (resp. without) successor available is equivalent to UTL+ with (resp. without) the "next" operator X available. This shows that despite previous negative results, the class of FO+-definable languages exhibits some form of robustness. We then exhibit an example of an FO-definable monotone language on one predicate, that is not FO+-definable, refining the example from [Kuperberg 2023] with 3 predicates. Moreover, we show that such a counter-example cannot be FO2-definable.
Mots clés
2012 ACM Subject Classification Theory of computation → Modal and temporal logics Theory of computation → Regular languages Theory Positive logic
LTL
separation
first-order
monotone Digital Object Identifier 10.4230/LIPIcs.CVIT.2016.23
2012 ACM Subject Classification Theory of computation → Modal and temporal logics
Theory of computation → Regular languages
Theory Positive logic
Domaines
Théorie et langage formel [cs.FL]Origine | Fichiers produits par l'(les) auteur(s) |
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