# 1. Foreword

Why3 is a platform for deductive program verification. It provides a rich language for specification and programming, called WhyML, and relies on external theorem provers, both automated and interactive, to discharge verification conditions. Why3 comes with a standard library of logical theories (integer and real arithmetic, Boolean operations, sets and maps, etc.) and basic programming data structures (arrays, queues, hash tables, etc.). A user can write WhyML programs directly and get correct-by-construction OCaml programs through an automated extraction mechanism. WhyML is also used as an intermediate language for the verification of C, Java, Rust, and Ada programs.

Why3 is a complete reimplementation of the former Why platform [FM07]. Among the new features are: numerous extensions to the input language, a new architecture for calling external provers, and a well-designed API, allowing to use Why3 as a software library. An important emphasis is put on modularity and genericity, giving the end user a possibility to easily reuse Why3 formalizations or to add support for a new external prover if wanted.

## 1.1. Availability

Why3 project page is https://www.why3.org/. The latest release is available there, in source format, together with this documentation and several examples.

Why3 is also distributed under the form of an OPAM package and a Debian package.

Why3 is distributed as open source and freely available under the terms of the GNU LGPL 2.1. See the file `LICENSE`.

See the file `INSTALL.md` for quick installation instructions, and Section 4 of this document for more detailed instructions.

## 1.2. Contact

There is a Zulip discussion forum for users’ discussion: https://why3.zulipchat.com/ together with a public mailing list: https://groupes.renater.fr/sympa/info/why3-club.

Report any bug to the Why3 Bug Tracking System (if you have an account there): https://gitlab.inria.fr/why3/why3/issues or to the Zulip forum.

## 1.3. Acknowledgements

We gratefully thank the people who contributed to Why3, directly or indirectly: Lucas Baudin, Benedikt Becker, Cláudio Belo Lourenço, Stefan Berghofer, Sylvie Boldo, Paul Bonnot, Martin Clochard, Guillaume Cluzel, Simon Cruanes, Sylvain Dailler, Xavier Denis, Yacine El Haddad, Clément Fumex, Quentin Garchery, Léon Gondelman, David Hauzar, Daisuke Ishii, Benjamin Jorge, Jacques-Henri Jourdan, Johannes Kanig, Mikhail Mandrykin, Matteo Manighetti, David Mentré, Benjamin Monate, Solène Moreau, Kim Nguyen, Thi-Minh-Tuyen Nguyen, Paul Patault, Mário Pereira, Gérald Point, Raphaël Rieu-Helft, Gabriel Scherer, Simão Melo de Sousa, Asma Tafat, Piotr Trojanek, Makarius Wenzel.