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Documents authored by Åman Pohjola, Johannes

Document
DOI: 10.4230/LIPIcs.ITP.2022.15
A Verified Cyclicity Checker: For Theories with Overloaded Constants

Authors: Arve Gengelbach and Johannes Åman Pohjola

Published in: LIPIcs, Volume 237, 13th International Conference on Interactive Theorem Proving (ITP 2022)

Abstract
Non-terminating (dependencies of) definitions can lead to logical contradictions, for example when defining a boolean constant as its own negation. Some proof assistants thus detect and disallow non-terminating definitions. Termination is generally undecidable when constants may have different definitions at different type instances, which is called (ad-hoc) overloading. The Isabelle/HOL proof assistant supports overloading of constant definitions, but relies on an unclear foundation for this critical termination check. With this paper we aim to close this gap: we present a mechanised proof that, for restricted overloading, non-terminating definitions are of a detectable cyclic shape, and we describe a mechanised algorithm with its correctness proof. In addition we demonstrate this cyclicity checker on parts of the Isabelle/HOL main library. Furthermore, we introduce the first-ever formally verified kernel of a proof assistant for higher-order logic with overloaded definitions. All our results are formalised in the HOL4 theorem prover.
Cite as

Arve Gengelbach and Johannes Åman Pohjola. A Verified Cyclicity Checker: For Theories with Overloaded Constants. In 13th International Conference on Interactive Theorem Proving (ITP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 237, pp. 15:1-15:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{gengelbach_et_al:LIPIcs.ITP.2022.15,
  author =	{Gengelbach, Arve and \r{A}man Pohjola, Johannes},
  title =	{{A Verified Cyclicity Checker: For Theories with Overloaded Constants}},
  booktitle =	{13th International Conference on Interactive Theorem Proving (ITP 2022)},
  pages =	{15:1--15:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-252-5},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{237},
  editor =	{Andronick, June and de Moura, Leonardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2022.15},
  URN =		{urn:nbn:de:0030-drops-167240},
  doi =		{10.4230/LIPIcs.ITP.2022.15},
  annote =	{Keywords: cyclicity, non-termination, ad-hoc overloading, definitions, Isabelle/HOL}
}
Document
DOI: 10.4230/LIPIcs.ITP.2019.32
Characteristic Formulae for Liveness Properties of Non-Terminating CakeML Programs

Authors: Johannes Åman Pohjola, Henrik Rostedt, and Magnus O. Myreen

Published in: LIPIcs, Volume 141, 10th International Conference on Interactive Theorem Proving (ITP 2019)

Abstract
There are useful programs that do not terminate, and yet standard Hoare logics are not able to prove liveness properties about non-terminating programs. This paper shows how a Hoare-like programming logic framework (characteristic formulae) can be extended to enable reasoning about the I/O behaviour of programs that do not terminate. The approach is inspired by transfinite induction rather than coinduction, and does not require non-terminating loops to be productive. This work has been developed in the HOL4 theorem prover and has been integrated into the ecosystem of proof tools surrounding the CakeML programming language.
Cite as

Johannes Åman Pohjola, Henrik Rostedt, and Magnus O. Myreen. Characteristic Formulae for Liveness Properties of Non-Terminating CakeML Programs. In 10th International Conference on Interactive Theorem Proving (ITP 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 141, pp. 32:1-32:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{amanpohjola_et_al:LIPIcs.ITP.2019.32,
  author =	{\r{A}man Pohjola, Johannes and Rostedt, Henrik and Myreen, Magnus O.},
  title =	{{Characteristic Formulae for Liveness Properties of Non-Terminating CakeML Programs}},
  booktitle =	{10th International Conference on Interactive Theorem Proving (ITP 2019)},
  pages =	{32:1--32:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-122-1},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{141},
  editor =	{Harrison, John and O'Leary, John and Tolmach, Andrew},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2019.32},
  URN =		{urn:nbn:de:0030-drops-110872},
  doi =		{10.4230/LIPIcs.ITP.2019.32},
  annote =	{Keywords: Program verification, non-termination, liveness, Hoare logic}
}
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