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Documents authored by Hur, Chung-Kil

Document
DOI: 10.4230/LIPIcs.CONCUR.2021.20
Formally Verified Simulations of State-Rich Processes Using Interaction Trees in Isabelle/HOL

Authors: Simon Foster, Chung-Kil Hur, and Jim Woodcock

Published in: LIPIcs, Volume 203, 32nd International Conference on Concurrency Theory (CONCUR 2021)

Abstract
Simulation and formal verification are important complementary techniques necessary in high assurance model-based systems development. In order to support coherent results, it is necessary to provide unifying semantics and automation for both activities. In this paper we apply Interaction Trees in Isabelle/HOL to produce a verification and simulation framework for state-rich process languages. We develop the core theory and verification techniques for Interaction Trees, use them to give a semantics to the CSP and Circus languages, and formally link our new semantics with the failures-divergences semantic model. We also show how the Isabelle code generator can be used to generate verified executable simulations for reactive and concurrent programs.
Cite as

Simon Foster, Chung-Kil Hur, and Jim Woodcock. Formally Verified Simulations of State-Rich Processes Using Interaction Trees in Isabelle/HOL. In 32nd International Conference on Concurrency Theory (CONCUR 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 203, pp. 20:1-20:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{foster_et_al:LIPIcs.CONCUR.2021.20,
  author =	{Foster, Simon and Hur, Chung-Kil and Woodcock, Jim},
  title =	{{Formally Verified Simulations of State-Rich Processes Using Interaction Trees in Isabelle/HOL}},
  booktitle =	{32nd International Conference on Concurrency Theory (CONCUR 2021)},
  pages =	{20:1--20:18},
  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.2021.20},
  URN =		{urn:nbn:de:0030-drops-143973},
  doi =		{10.4230/LIPIcs.CONCUR.2021.20},
  annote =	{Keywords: Coinduction, Process Algebra, Theorem Proving, Simulation}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2015.475
A Provably Correct Sampler for Probabilistic Programs

Authors: Chung-Kil Hur, Aditya V. Nori, Sriram K. Rajamani, and Selva Samuel

Published in: LIPIcs, Volume 45, 35th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2015)

Abstract
We consider the problem of inferring the implicit distribution specified by a probabilistic program. A popular inference technique for probabilistic programs called Markov Chain Monte Carlo or MCMC sampling involves running the program repeatedly and generating sample values by perturbing values produced in "previous runs". This simulates a Markov chain whose stationary distribution is the distribution specified by the probabilistic program. However, it is non-trivial to implement MCMC sampling for probabilistic programs since each variable could be updated at multiple program points. In such cases, it is unclear which values from the "previous run" should be used to generate samples for the "current run". We present an algorithm to solve this problem for the general case and formally prove that the algorithm is correct. Our algorithm handles variables that are updated multiple times along the same path, updated along different paths in a conditional statement, or repeatedly updated inside loops, We have implemented our algorithm in a tool called InferX. We empirically demonstrate that InferX produces the correct result for various benchmarks, whereas existing tools such as R2 and Stan produce incorrect results on several of these benchmarks.
Cite as

Chung-Kil Hur, Aditya V. Nori, Sriram K. Rajamani, and Selva Samuel. A Provably Correct Sampler for Probabilistic Programs. In 35th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 45, pp. 475-488, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{hur_et_al:LIPIcs.FSTTCS.2015.475,
  author =	{Hur, Chung-Kil and Nori, Aditya V. and Rajamani, Sriram K. and Samuel, Selva},
  title =	{{A Provably Correct Sampler for Probabilistic Programs}},
  booktitle =	{35th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2015)},
  pages =	{475--488},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-97-2},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{45},
  editor =	{Harsha, Prahladh and Ramalingam, G.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2015.475},
  URN =		{urn:nbn:de:0030-drops-56553},
  doi =		{10.4230/LIPIcs.FSTTCS.2015.475},
  annote =	{Keywords: Probabilistic Programming, Program Correctness, Probabilistic Inference, Markov Chain Monte Carlo Sampling}
}
Document
DOI: 10.4230/DagSemProc.10351.7
Step-Indexing: The Good, the Bad and the Ugly

Authors: Nick Benton and Chung-Kil Hur

Published in: Dagstuhl Seminar Proceedings, Volume 10351, Modelling, Controlling and Reasoning About State (2010)

Abstract
Over the last decade, step-indices have been widely used for the construction of operationally-based logical relations in the presence of various kinds of recursion. We first give an argument that step-indices, or something like them, seem to be required for defining realizability relations between high-level source languages and low-level targets, in the case that the low-level allows egregiously intensional operations such as reflection or comparison of code pointers. We then show how, much to our annoyance, step-indices also seem to prevent us from exploiting such operations as aggressively as we would like in proving program transformations.
Cite as

Nick Benton and Chung-Kil Hur. Step-Indexing: The Good, the Bad and the Ugly. In Modelling, Controlling and Reasoning About State. Dagstuhl Seminar Proceedings, Volume 10351, pp. 1-9, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{benton_et_al:DagSemProc.10351.7,
  author =	{Benton, Nick and Hur, Chung-Kil},
  title =	{{Step-Indexing: The Good, the Bad and the Ugly}},
  booktitle =	{Modelling, Controlling and Reasoning About State},
  pages =	{1--9},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2010},
  volume =	{10351},
  editor =	{Amal Ahmed and Nick Benton and Lars Birkedal and Martin Hofmann},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.10351.7},
  URN =		{urn:nbn:de:0030-drops-28085},
  doi =		{10.4230/DagSemProc.10351.7},
  annote =	{Keywords: Step-Indexing, Logical Relations, Low-Level Languages, Compiler Correctness}
}
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