The Probabilistic Computational Tree Logic (PCTL) is the main specification formalism for discrete probabilistic systems modeled by Markov chains. Despite serious research attempts, the decidability of PCTL satisfiability and validity problems remained unresolved for 30 years. We show that both problems are highly undecidable, i.e., beyond the arithmetical hierarchy. Consequently, there is no sound and complete deductive system for PCTL.
@InProceedings{chodil_et_al:LIPIcs.ICALP.2025.151, author = {Chodil, Miroslav and Ku\v{c}era, Anton{\'\i}n}, title = {{The Satisfiability and Validity Problems for Probabilistic Computational Tree Logic Are Highly Undecidable}}, booktitle = {52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)}, pages = {151:1--151:20}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-372-0}, ISSN = {1868-8969}, year = {2025}, volume = {334}, editor = {Censor-Hillel, Keren and Grandoni, Fabrizio and Ouaknine, Jo\"{e}l and Puppis, Gabriele}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2025.151}, URN = {urn:nbn:de:0030-drops-235281}, doi = {10.4230/LIPIcs.ICALP.2025.151}, annote = {Keywords: Satisfiability, temporal logics, probabilistic CTL} }
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