November 6, 2008, Providence, RI---New computer tools have the
potential to revolutionize the practice of mathematics by providing
far more-reliable proofs of mathematical results than have ever been
possible in the history of humankind. These computer tools, based on
the notion of "formal proof", have in recent years been used to
provide nearly infallible proofs of many important results in
mathematics. A ground-breaking collection of four articles by leading
experts, published today in the *Notices of the American Mathematical
Society* (http://www.ams.org/notices), explores new developments in the use of formal proof in mathematics.

When mathematicians prove theorems in the traditional way, they present the argument in narrative form. They assume previous results, they gloss over details they think other experts will understand, they take shortcuts to make the presentation less tedious, they appeal to intuition, etc. The correctness of the arguments is determined by the scrutiny of other mathematicians, in informal discussions, in lectures, or in journals. It is sobering to realize that the means by which mathematical results are verified is essentially a social process and is thus fallible. When it comes to central, well known results, the proofs are especially well checked and errors are eventually found. Nevertheless the history of mathematics has many stories about false results that went undetected for a long time. In addition, in some recent cases, important theorems have required such long and complicated proofs that very few people have the time, energy, and necessary background to check through them. And some proofs contain extensive computer code to, for example, check a lot of cases that would be infeasible to check by hand. How can mathematicians be sure that such proofs are reliable?

To get around these problems, computer scientists and mathematicians began to develop the field of formal proof. A formal proof is one in which every logical inference has been checked all the way back to the fundamental axioms of mathematics. Mathematicians do not usually write formal proofs because such proofs are so long and cumbersome that it would be impossible to have them checked by human mathematicians. But now one can get "computer proof assistants" to do the checking. In recent years, computer proof assistants have become powerful enough to handle difficult proofs.

Only in simple cases can one feed a statement to a computer proof assistant and expect it to hand over a proof. Rather, the mathematician has to know how to prove the statement; the proof then is greatly expanded into the special syntax of formal proof, with every step spelled out, and it is this formal proof that the computer checks. It is also possible to let computers loose to explore mathematics on their own, and in some cases they have come up with interesting conjectures that went unnoticed by mathematicians. We may be close to seeing how computers, rather than humans, would do mathematics.

The four *Notices* articles explore the current state of the art of
formal proof and provide practical guidance for using computer proof
assistants. If the use of these assistants becomes widespread, they
could change deeply mathematics as it is currently practiced. One
long-term dream is to have formal proofs of all of the central
theorems in mathematics. Thomas Hales, one of the authors writing in
the Notices, says that such a collection of proofs would be akin to
"the sequencing of the mathematical genome".

**The four articles are:**

- Formal Proof, by Thomas Hales, University of Pittsburgh
- Formal Proof---Theory and Practice, by John Harrison, Intel Corporation
- Formal proof---The Four Colour Theorem, by Georges Gonthier, Microsoft Research, Cambridge, England
- Formal Proof---Getting Started, by Freek Wiedijk, Radboud University, Nijmegen, Netherlands

The articles appear today in the December 2008 issue of the *Notice*s
and are freely available at http://www.ams.org/notices.

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#### Journal

Notices of the American Mathematical Society