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Fixpoint Logic with Chop (FLC) extends the modal μ-calculus with an operator for sequential composition between predicate transformers. This makes it an expressive modal fixpoint logic which is capable of formalising many non-regular program properties. Its satisfiability problem is highly undecidable. Here we define Visibly Pushdown Fixpoint Logic with Chop, a fragment in which fixpoint formulas are required to be of a certain form resembling visibly pushdown grammars. We give a sound and complete game-theoretic characterisation of FLC’s satisfiability problem and show that the games corresponding to formulas from this fragment are stair-parity games and therefore effectively solvable, resulting in 2EXPTIME-completeness of this fragment. The lower bound is inherited from PDL over Recursive Programs, which is structurally similar but considerably weaker in expressive power.
@InProceedings{bruse_et_al:LIPIcs.CONCUR.2021.23,
author = {Bruse, Florian and Lange, Martin},
title = {{A Decidable Non-Regular Modal Fixpoint Logic}},
booktitle = {32nd International Conference on Concurrency Theory (CONCUR 2021)},
pages = {23:1--23:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-203-7},
ISSN = {1868-8969},
year = {2021},
volume = {203},
editor = {Haddad, Serge and Varacca, Daniele},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2021.23},
URN = {urn:nbn:de:0030-drops-144003},
doi = {10.4230/LIPIcs.CONCUR.2021.23},
annote = {Keywords: formal specification, temporal logic, expressive power}
}