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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, or Ada programs.

Why3 is a complete reimplementation of the former Why platform [5]. 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.


Why3 project page is http://why3.lri.fr/. The last distribution is available there, in source format, together with this documentation and several examples.

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 for quick installation instructions, and Section 5 of this document for more detailed instructions.


There is a public mailing list for users’ discussions: http://lists.gforge.inria.fr/mailman/listinfo/why3-club.

Report any bug to the Why3 Bug Tracking System: https://gforge.inria.fr/tracker/?atid=10293&group_id=2990&func=browse.


We gratefully thank the people who contributed to Why3, directly or indirectly: Romain Bardou, Stefan Berghofer, Sylvie Boldo, Martin Clochard, Simon Cruanes, Leon Gondelman, Johannes Kanig, Stéphane Lescuyer, David Mentré, Simão Melo de Sousa, Benjamin Monate, Thi-Minh-Tuyen Nguyen, Asma Tafat, Piotr Trojanek.

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