Abstract
CSI is a strong automated confluence prover for rewrite systems which has been in development since 2010. In this paper we report on recent extensions that make CSI more powerful, secure, and useful. These extensions include improved confluence criteria but also support for uniqueness of normal forms. Most of the implemented techniques produce machine-readable proof output that can be independently verified by an external tool, thus increasing the trust in CSI. We also report on CSI\(\mathbf {\hat{~}}\)oho, a tool built on the same framework and similar ideas as CSI that automatically checks confluence of higher-order rewrite systems.
This research is supported by FWF (Austrian Science Fund) project P27528.
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Notes
- 1.
Available from http://coco.nue.riec.tohoku.ac.jp/2013, http://coco.nue.riec.tohoku.ac.jp/2014, http://coco.nue.riec.tohoku.ac.jp/2015, http://coco.nue.riec.tohoku.ac.jp/2016, under Entrants.
- 2.
- 3.
- 4.
In fact, CSI uses a modified definition of \(\mathcal {S}^e\) that avoids adding extended rules for rules where the same linear variable appears as an argument of the two top-flattenings of the left-hand and right-hand sides of the rule, using the same AC symbol. In the example, this applies to the first two rules. We still have \({\rightarrow _{\mathcal {S}/\mathsf {AC}}} = {\rightarrow _{\mathcal {S}^e,\mathsf {AC}}} \cdot \sim _\mathsf {AC}\).
- 5.
This can be shown using tree automata techniques [11].
- 6.
A term is a pattern if free variables only have distinct bound variables as arguments.
- 7.
A development step
contracts multiple, non-overlapping but possibly nested redexes at once.
- 8.
IsaFoR/CeTA and CPF are available at http://cl-informatik.uibk.ac.at/software/ceta.
- 9.
Full details are available from CSI’s website.
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Acknowledgments
We thank Sarah Winkler for contributing code and expertise related to AC termination and AC critical pairs.
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Nagele, J., Felgenhauer, B., Middeldorp, A. (2017). CSI: New Evidence – A Progress Report. In: de Moura, L. (eds) Automated Deduction – CADE 26. CADE 2017. Lecture Notes in Computer Science(), vol 10395. Springer, Cham. https://doi.org/10.1007/978-3-319-63046-5_24
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