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We study the impact of adding both counting quantifiers and a single transitive relation to the fluted fragment - a fragment of first-order logic originating in the work of W.V.O. Quine. The resulting formalism can be viewed as a multi-variable, non-guarded extension of certain systems of description logic featuring number restrictions and transitive roles, but lacking role-inverses. We establish the finite model property for our logic, and show that the satisfiability problem for its k-variable sub-fragment is in (k+1)-NExpTime. We also derive ExpSpace-hardness of the satisfiability problem for the two-variable, fluted fragment with one transitive relation (but without counting quantifiers), and prove that, when a second transitive relation is allowed, both the satisfiability and the finite satisfiability problems for the two-variable fluted fragment with counting quantifiers become undecidable.
@InProceedings{pratthartmann_et_al:LIPIcs.CSL.2023.32,
author = {Pratt-Hartmann, Ian and Tendera, Lidia},
title = {{Adding Transitivity and Counting to the Fluted Fragment}},
booktitle = {31st EACSL Annual Conference on Computer Science Logic (CSL 2023)},
pages = {32:1--32:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-264-8},
ISSN = {1868-8969},
year = {2023},
volume = {252},
editor = {Klin, Bartek and Pimentel, Elaine},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2023.32},
URN = {urn:nbn:de:0030-drops-174933},
doi = {10.4230/LIPIcs.CSL.2023.32},
annote = {Keywords: fluted logic, transitivity, counting, satisfiability, decidability, complexity}
}