The Coq Proof Assistant

Coq is a formal proof management system. It provides a formal language to write mathematical definitions, executable algorithms and theorems together with an environment for semi-interactive development of machine-checked proofs. Typical applications include the certification of properties of programming languages (e.g. the CompCert compiler certification project, the Verified Software Toolchain for verification of C programs, or the Iris framework for concurrent separation logic), the formalization of mathematics (e.g. the full formalization of the Feit-Thompson theorem, or homotopy type theory), and teaching.

Coq version 8.20 adds a new rewrite rule mechanism along with a few new features, a host of improvements to the virtual machine, the notation system, Ltac2 and the standard library.

We highlight some of the most impactful changes here:

Notable breaking changes:

See the Changes in 8.20.0 section below for the detailed list of changes, including potentially breaking changes marked with Changed. Coq's reference manual for 8.20, documentation of the 8.20 standard library and developer documentation of the 8.20 ML API are also available.

Théo Zimmermann with help from Ali Caglayan and Jason Gross maintained coqbot used to run Coq's CI and other pull request management tasks.

Jason Gross maintained the bug minimizer and its automatic use through coqbot.

Erik Martin-Dorel maintained the Coq Docker images and the docker-keeper compiler used to build and keep those images up to date (note that the tool is not Coq specific). Cyril Cohen, Vincent Laporte, Pierre Roux and Théo Zimmermann maintained the Nix toolbox used by many Coq projects for continuous integration.

Ali Caglayan, Emilio Jesús Gallego Arias, Rudi Grinberg and Rodolphe Lepigre maintained the Dune build system for OCaml and Coq used to build Coq itself and many Coq projects.

The opam repository for Coq packages has been maintained by Guillaume Claret, Guillaume Melquiond, Karl Palmskog and Enrico Tassi with contributions from many users. A list of packages is available on the Coq website.

Coq 8.20 was made possible thanks to the following reviewers: Frédéric Besson, Lasse Blaauwbroek, Ali Caglayan, Cyril Cohen, Andrej Dudenhefner, Andres Erbsen, Jim Fehrle, Emilio Jesús Gallego Arias, Gaëtan Gilbert, Jason Gross, Hugo Herbelin, Ralf Jung, Jan-Oliver Kaiser, Chantal Keller, Olivier Laurent, Rodolphe Lepigre, Yishuai Li, Ralph Matthes, Guillaume Melquiond, Pierre-Marie Pédrot, Karl Palmskog, Clément Pit-Claudel, Pierre Rousselin, Pierre Roux, Michael Soegtrop, soukouki, Matthieu Sozeau, Nicolas Tabareau, Enrico Tassi, Niels van der Weide, Nickolai Zeldovich and Théo Zimmermann. See the Coq Team face book page for more details on Coq's development team.

The 59 contributors to the 8.20 version are: Timur Aminev, Frédéric Besson, Lasse Blaauwbroek, Björn Brandenburg, Ali Caglayan, Nikolaos Chatzikonstantinou, Sylvain Chiron, chluebi, Cyril Cohen, Anton Danilkin, Louise Dubois de Prisque, Andrej Dudenhefner, Maxime Dénès, Andres Erbsen, Jim Fehrle, Davide Fissore, Andreas Florath, Yannick Forster, Mario Frank, Gaëtan Gilbert, Georges Gonthier, Jason Gross, Stefan Haan, Hugo Herbelin, Lennart Jablonka, Emilio Jesús Gallego Arias, Ralf Jung, Jan-Oliver Kaiser, Evgenii Kosogorov, Rodolphe Lepigre, Yann Leray, David M. Cooke, Erik Martin-Dorel, Guillaume Melquiond, Guillaume Munch-Maccagnoni, Karl Palmskog, Julien Puydt, Pierre-Marie Pédrot, Ramkumar Ramachandra, Pierre Rousselin, Pierre Roux, Kazuhiko Sakaguchi, Bernhard Schommer, Remy Seassau, Matthieu Sozeau, Enrico Tassi, Romain Tetley, Laurent Théry, Alexey Trilis, Oliver Turner, Quentin Vermande, Li-yao Xia and Théo Zimmermann,

The Coq community at large helped improve this new version via the GitHub issue and pull request system, the coq-club@inria.fr mailing list, the Discourse forum and the Coq Zulip chat.

Version 8.20's development spanned 7 months from the release of Coq 8.19.0 (9 months since the branch for 8.19.0). Pierre Roux and Guillaume Melquiond are the release managers of Coq 8.20. This release is the result of 470 merged PRs, closing 113 issues.