The precise identification of the expressive power of logic languages used in formal methods for specifying and verifying run-time properties of critical systems is a fundamental task and characterisation theorems play a crucial role as model-theoretic tools in this regard. While a clear picture of the expressive power of linear-time temporal logics in terms of word automata and predicate logics has long been established, a complete mapping of the corresponding relationships for branching-time temporal logics has proven to be a more elusive task over the past four decades with few scattered results. Only recently, an automata-theoretic characterisation of both CTL* and its full-ω-regular extension ECTL* has been provided in terms of Symmetric Hesitant Tree Automata (HTA), with and without a suitable counter-freeness restriction on their linear behaviours. These two temporal logics also correspond to the bisimulation-invariant semantic fragments of Monadic Path Logic (MPL) and Monadic Chain Logic (MCL), respectively. Additionally, it has been proven that the counting extensions of CTL* and ECTL*, namely CCTL* and CECTL*, enjoy equivalent graded versions of the HTAs for the corresponding non-counting logics. However, while Moller and Rabinovich have proved CCTL* to be equivalent to full MPL, thus filling the gap for the standard branching-time logic, no similar result has been given for CECTL*. This work completes the picture, by proving the expressive equivalence of CECTL* and full MCL, by means of a composition theorem for the latter logic. This also indirectly establishes the equivalence between HTAs and their first-order extensions HFTAs, as originally introduced by Walukiewicz.
@InProceedings{benerecetti_et_al:LIPIcs.TIME.2024.18, author = {Benerecetti, Massimo and Bozzelli, Laura and Mogavero, Fabio and Peron, Adriano}, title = {{Full Characterisation of Extended CTL*}}, booktitle = {31st International Symposium on Temporal Representation and Reasoning (TIME 2024)}, pages = {18:1--18:18}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-349-2}, ISSN = {1868-8969}, year = {2024}, volume = {318}, editor = {Sala, Pietro and Sioutis, Michael and Wang, Fusheng}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2024.18}, URN = {urn:nbn:de:0030-drops-212259}, doi = {10.4230/LIPIcs.TIME.2024.18}, annote = {Keywords: Branching-Time Temporal Logics, Monadic Chain Logic, Tree Automata} }
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