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A Formalization of Dedekind Domains and Class Groups of Global Fields

Authors Anne Baanen , Sander R. Dahmen , Ashvni Narayanan , Filippo A. E. Nuccio Mortarino Majno di Capriglio

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Author Details

Anne Baanen
  • Department of Computer Science, Vrije Universiteit Amsterdam, The Netherlands
Sander R. Dahmen
  • Department of Mathematics, Vrije Universiteit Amsterdam, The Netherlands
Ashvni Narayanan
  • London School of Geometry and Number Theory, UK
Filippo A. E. Nuccio Mortarino Majno di Capriglio
  • Univ Lyon, Université Jean Monnet Saint-Étienne, CNRS UMR 5208, Institut Camille Jordan, F-42023 Saint-Étienne, France


We would like to thank Jasmin Blanchette and the anonymous reviewers for useful comments on previous versions of the manuscript, which found their way into this paper. A. N. would like to thank Prof. Kevin Buzzard for his constant support and encouragement, and for introducing her to the other co-authors. A. N. and F. N. wish to express their deepest gratitude to Anne Baanen for the generosity shown along all stages of the project. Without Anne’s never-ending patience, it would have been impossible for them to contribute to this project, and to overcome several difficulties. Finally, we would like to thank the whole mathlib community for invaluable advice all along the project.

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Anne Baanen, Sander R. Dahmen, Ashvni Narayanan, and Filippo A. E. Nuccio Mortarino Majno di Capriglio. A Formalization of Dedekind Domains and Class Groups of Global Fields. In 12th International Conference on Interactive Theorem Proving (ITP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 193, pp. 5:1-5:19, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2021)


Dedekind domains and their class groups are notions in commutative algebra that are essential in algebraic number theory. We formalized these structures and several fundamental properties, including number theoretic finiteness results for class groups, in the Lean prover as part of the mathlib mathematical library. This paper describes the formalization process, noting the idioms we found useful in our development and mathlib’s decentralized collaboration processes involved in this project.

Subject Classification

ACM Subject Classification
  • Mathematics of computing → Mathematical software
  • Security and privacy → Logic and verification
  • formal math
  • algebraic number theory
  • commutative algebra
  • Lean
  • mathlib


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