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<?xml version='1.0' encoding='iso-8859-1' ?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<!-- $Id$ -->
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<title>Overview</title>
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<?include file="//include/navigation.include.html"?>
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<div id="content">
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<h2>What is Isabelle?</h2>
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<p>
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Isabelle is a generic proof assistant. It allows mathematical
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formulas to be expressed in a formal language and provides tools
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for proving those formulas in a logical calculus. The main
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application is the formalization of mathematical proofs and in
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particular <em>formal verification</em>, which includes proving
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the correctness of computer hardware or software and proving
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properties of computer languages and protocols.</p>
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<p>Compared with similar tools, Isabelle's distinguishing feature is its
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flexibility. Most proof assistants are built around a single formal calculus,
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typically higher-order logic. Isabelle has the capacity to accept a variety
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of formal calculi. The distributed version supports higher-order logic but
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also axiomatic set theory and several other formalisms. See
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<a href="logics.html">logics</a> for more details.</p>
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<p>Isabelle is a joint project between Lawrence C. Paulson
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(University of Cambridge, UK) and Tobias Nipkow (Technical
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University of Munich, Germany).</p>
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<p>Isabelle is distributed <em>freely</em> as Open Source
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Software <!--a href="//dist/Isabelle/COPYRIGHT"-->BSD
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license<!--/a-->; see the <a
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href="installation.html">installation instructions</a>.</p>
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<h2>Preview of Isabelle</h2>
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<a href="//media/pg_preview.mov">
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<img class="left" src="//img/screenshot_isabelle_pg.png" alt="Isabelle Screenshot"
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width="250" height="277" />
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</a>
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<p>Here is a <a href="//media/pg_preview.mov">hyperlinked preview</a> demonstrating
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Isabelle and ProofGeneral, in <a href="http://www.apple.com/quicktime/download/">QuickTime
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format</a>, and also as a <a href="//media/pg_preview.pdf">non-hyperlinked preview</a> in PDF.</p>
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<br clear="all"/>
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<h2>What Isabelle offers</h2>
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<p>Isabelle provides excellent notational support: new notations
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can be introduced, using normal mathematical symbols. Proofs can
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be written in a structured notation based upon traditional proof
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style, or more straightforwardly as sequences of
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commands. Definitions and proofs may include TeX source, from
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which Isabelle can automatically generate typeset documents.</p>
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<p>The main limitation of all such proof systems is that proving
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theorems requires much effort from an expert user. Isabelle
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incorporates some tools to improve the user's productivity by
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automating some parts of the proof process. In particular,
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Isabelle's <em>classical reasoner</em> can perform long chains
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of reasoning steps to prove formulas. The <em>simplifier</em>
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can reason with and about equations. Linear <em>arithmetic</em>
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facts are proved automatically.</p>
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<p>Isabelle comes with a large theory library of formally
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verified mathematics, including elementary number theory (for
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example, Gauss's law of quadratic reciprocity), analysis (basic
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properties of limits, derivatives and integrals), algebra (up to
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Sylow's theorem) and set theory (the relative consistency of the
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Axiom of Choice). Also provided are numerous examples arising
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from research into formal verification.</p>
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<p>With <em>Isar</em>, Isabelle offers a concise proof formulation language
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which enables a user to write proof scripts naturally understandable for
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both humans <em>and</em> computers.</p>
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<p>Isabelle is closely integrated with the <a href=
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"http://proofgeneral.inf.ed.ac.uk/">ProofGeneral</a> user interface, which
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eases the task of writing and maintaining proof scripts.</p>
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<p>Ample <a href="documentation.html">documentation</a> is available
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about using Isabelle and its inner concepts, including a
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<a href="http://www4.in.tum.de/~nipkow/LNCS2283/">Tutorial</a> published by
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Springer-Verlag.</p>
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</div>
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<div class="hr"><hr/></div>
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<?include file="//include/footer.include.html"?>
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</body>
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</html>
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