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Documents authored by Norrish, Michael


Document
Dependently Sorted Theorem Proving for Mathematical Foundations

Authors: Yiming Xu and Michael Norrish

Published in: LIPIcs, Volume 268, 14th International Conference on Interactive Theorem Proving (ITP 2023)


Abstract
We describe a new meta-logical system for mechanising foundations of mathematics. Using dependent sorts and first order logic, our system (implemented as an LCF-style theorem-prover) improves on the state-of-the-art by providing efficient type-checking, convenient automatic rewriting and interactive proof support. We assess our implementation by axiomatising Lawvere’s Elementary Theory of the Category of Sets (ETCS) [F. William Lawvere, 1964], and Shulman’s Sets, Elements and Relations (SEAR) [Michael Shulman, 2022]. We then demonstrate our system’s ability to perform some basic mathematical constructions such as quotienting, induction and coinduction by constructing integers, lists and colists. We also compare with some existing work on modal model theory done in HOL4 [Yiming Xu and Michael Norrish, 2020]. Using the analogue of type-quantification, we are able to prove a theorem that this earlier work could not. Finally, we show that SEAR can construct sets that are larger than any finite iteration of the power set operation. This shows that SEAR, unlike HOL, can construct sets beyond V_{ω+ω}.

Cite as

Yiming Xu and Michael Norrish. Dependently Sorted Theorem Proving for Mathematical Foundations. In 14th International Conference on Interactive Theorem Proving (ITP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 268, pp. 33:1-33:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


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@InProceedings{xu_et_al:LIPIcs.ITP.2023.33,
  author =	{Xu, Yiming and Norrish, Michael},
  title =	{{Dependently Sorted Theorem Proving for Mathematical Foundations}},
  booktitle =	{14th International Conference on Interactive Theorem Proving (ITP 2023)},
  pages =	{33:1--33:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-284-6},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{268},
  editor =	{Naumowicz, Adam and Thiemann, Ren\'{e}},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2023.33},
  URN =		{urn:nbn:de:0030-drops-184085},
  doi =		{10.4230/LIPIcs.ITP.2023.33},
  annote =	{Keywords: first order logic, sorts, structural set theory, mechanised mathematics, foundation of mathematics, category theory}
}
Document
Kalas: A Verified, End-To-End Compiler for a Choreographic Language

Authors: Johannes Åman Pohjola, Alejandro Gómez-Londoño, James Shaker, and Michael Norrish

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


Abstract
Choreographies are an abstraction for globally describing deadlock-free communicating systems. A choreography can be compiled into multiple endpoints preserving the global behavior, providing a path for concrete system implementations. Of course, the soundness of this approach hinges on the correctness of the compilation function. In this paper, we present a verified compiler for Kalas, a choreographic language. Its machine-checked end-to-end proof of correctness ensures all generated endpoints adhere to the system description, preserving the top-level communication guarantees. This work uses the verified CakeML compiler and Hol4 proof assistant, allowing for concrete executable implementations and statements of correctness at the machine code level for multiple architectures.

Cite as

Johannes Åman Pohjola, Alejandro Gómez-Londoño, James Shaker, and Michael Norrish. Kalas: A Verified, End-To-End Compiler for a Choreographic Language. In 13th International Conference on Interactive Theorem Proving (ITP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 237, pp. 27:1-27:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


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@InProceedings{pohjola_et_al:LIPIcs.ITP.2022.27,
  author =	{Pohjola, Johannes \r{A}man and G\'{o}mez-Londo\~{n}o, Alejandro and Shaker, James and Norrish, Michael},
  title =	{{Kalas: A Verified, End-To-End Compiler for a Choreographic Language}},
  booktitle =	{13th International Conference on Interactive Theorem Proving (ITP 2022)},
  pages =	{27:1--27:18},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2022.27},
  URN =		{urn:nbn:de:0030-drops-167368},
  doi =		{10.4230/LIPIcs.ITP.2022.27},
  annote =	{Keywords: Choreographies, Interactive Theorem Proving, Compiler Verification}
}
Document
Mechanizing Soundness of Off-Policy Evaluation

Authors: Jared Yeager, J. Eliot B. Moss, Michael Norrish, and Philip S. Thomas

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


Abstract
There are reinforcement learning scenarios - e.g., in medicine - where we are compelled to be as confident as possible that a policy change will result in an improvement before implementing it. In such scenarios, we can employ off-policy evaluation (OPE). The basic idea of OPE is to record histories of behaviors under the current policy, and then develop an estimate of the quality of a proposed new policy, seeing what the behavior would have been under the new policy. As we are evaluating the policy without actually using it, we have the "off-policy" of OPE. Applying a concentration inequality to the estimate, we derive a confidence interval for the expected quality of the new policy. If the confidence interval lies above that of the current policy, we can change policies with high confidence that we will do no harm. We focus here on the mathematics of this method, by mechanizing the soundness of off-policy evaluation. A natural side effect of the mechanization is both to clarify all the result’s mathematical assumptions and preconditions, and to further develop HOL4’s library of verified statistical mathematics, including concentration inequalities. Of more significance, the OPE method relies on importance sampling, whose soundness we prove using a measure-theoretic approach. In fact, we generalize the standard result, showing it for contexts comprising both discrete and continuous probability distributions.

Cite as

Jared Yeager, J. Eliot B. Moss, Michael Norrish, and Philip S. Thomas. Mechanizing Soundness of Off-Policy Evaluation. In 13th International Conference on Interactive Theorem Proving (ITP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 237, pp. 32:1-32:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


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@InProceedings{yeager_et_al:LIPIcs.ITP.2022.32,
  author =	{Yeager, Jared and Moss, J. Eliot B. and Norrish, Michael and Thomas, Philip S.},
  title =	{{Mechanizing Soundness of Off-Policy Evaluation}},
  booktitle =	{13th International Conference on Interactive Theorem Proving (ITP 2022)},
  pages =	{32:1--32:20},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2022.32},
  URN =		{urn:nbn:de:0030-drops-167413},
  doi =		{10.4230/LIPIcs.ITP.2022.32},
  annote =	{Keywords: Formal Methods, HOL4, Reinforcement Learning, Off-Policy Evaluation, Concentration Inequality, Hoeffding}
}
Document
A Verified Compositional Algorithm for AI Planning

Authors: Mohammad Abdulaziz, Charles Gretton, and Michael Norrish

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


Abstract
We report on our HOL4 verification of an AI planning algorithm. The algorithm is compositional in the following sense: a planning problem is divided into multiple smaller abstractions, then each of the abstractions is solved, and finally the abstractions' solutions are composed into a solution for the given problem. Formalising the algorithm, which was already quite well understood, revealed nuances in its operation which could lead to computing buggy plans. The formalisation also revealed that the algorithm can be presented more generally, and can be applied to systems with infinite states and actions, instead of only finite ones. Our formalisation extends an earlier model for slightly simpler transition systems, and demonstrates another step towards formal treatments of more and more of the algorithms and reasoning used in AI planning, as well as model checking.

Cite as

Mohammad Abdulaziz, Charles Gretton, and Michael Norrish. A Verified Compositional Algorithm for AI Planning. In 10th International Conference on Interactive Theorem Proving (ITP 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 141, pp. 4:1-4:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)


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@InProceedings{abdulaziz_et_al:LIPIcs.ITP.2019.4,
  author =	{Abdulaziz, Mohammad and Gretton, Charles and Norrish, Michael},
  title =	{{A Verified Compositional Algorithm for AI Planning}},
  booktitle =	{10th International Conference on Interactive Theorem Proving (ITP 2019)},
  pages =	{4:1--4:19},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2019.4},
  URN =		{urn:nbn:de:0030-drops-110596},
  doi =		{10.4230/LIPIcs.ITP.2019.4},
  annote =	{Keywords: AI Planning, Compositional Algorithms, Algorithm Verification, Transition Systems}
}
Document
Draining the Swamp: Micro Virtual Machines as Solid Foundation for Language Development

Authors: Kunshan Wang, Yi Lin, Stephen M. Blackburn, Michael Norrish, and Antony L. Hosking

Published in: LIPIcs, Volume 32, 1st Summit on Advances in Programming Languages (SNAPL 2015)


Abstract
Many of today's programming languages are broken. Poor performance, lack of features and hard-to-reason-about semantics can cost dearly in software maintenance and inefficient execution. The problem is only getting worse with programming languages proliferating and hardware becoming more complicated. An important reason for this brokenness is that much of language design is implementation-driven. The difficulties in implementation and insufficient understanding of concepts bake bad designs into the language itself. Concurrency, architectural details and garbage collection are three fundamental concerns that contribute much to the complexities of implementing managed languages. We propose the micro virtual machine, a thin abstraction designed specifically to relieve implementers of managed languages of the most fundamental implementation challenges that currently impede good design. The micro virtual machine targets abstractions over memory (garbage collection), architecture (compiler backend), and concurrency. We motivate the micro virtual machine and give an account of the design and initial experience of a concrete instance, which we call Mu, built over a two year period. Our goal is to remove an important barrier to performant and semantically sound managed language design and implementation.

Cite as

Kunshan Wang, Yi Lin, Stephen M. Blackburn, Michael Norrish, and Antony L. Hosking. Draining the Swamp: Micro Virtual Machines as Solid Foundation for Language Development. In 1st Summit on Advances in Programming Languages (SNAPL 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 32, pp. 321-336, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)


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@InProceedings{wang_et_al:LIPIcs.SNAPL.2015.321,
  author =	{Wang, Kunshan and Lin, Yi and Blackburn, Stephen M. and Norrish, Michael and Hosking, Antony L.},
  title =	{{Draining the Swamp: Micro Virtual Machines as Solid Foundation for Language Development}},
  booktitle =	{1st Summit on Advances in Programming Languages (SNAPL 2015)},
  pages =	{321--336},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-80-4},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{32},
  editor =	{Ball, Thomas and Bodík, Rastislav and Krishnamurthi, Shriram and Lerner, Benjamin S. and Morriset, Greg},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.SNAPL.2015.321},
  URN =		{urn:nbn:de:0030-drops-50341},
  doi =		{10.4230/LIPIcs.SNAPL.2015.321},
  annote =	{Keywords: virtual machines, concurrency, just-in-time compiling, garbage collection}
}
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