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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/htmlheader.include.html"?>
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</head>
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<body class="main">
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    <?include file="//include/header.include.html"?>
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    <div class="hr"><hr/></div>
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    <?include file="//include/navigation.include.html"?>
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    <div class="hr"><hr/></div>
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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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      <h2>What Isabelle offers</h2>
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        <a href="//img/isabelle_pg_screenshot_big.png">
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            <img class="left" src="//img/isabelle_pg_screenshot_small.png" alt="Sreenshot "
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                width="250" height="277" />
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        </a>
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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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      <br clear="all" />
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      <h2>Preview</h2>
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      <p>We provide 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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      <p>Ample <a href="dist/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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      <h2>Projects</h2>
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      <p>There is an (incomplete) list of past and present <a href=
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      "http://www.cl.cam.ac.uk/Research/HVG/Isabelle/projects.html">projects</a>
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      undertaken using Isabelle available.</p>
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      <h2>License</h2>
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      <p>Isabelle is distributed free of charge under the open source
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      <a href="dist/Isabelle/COPYRIGHT">BSD license</a>. You may use any of our <a
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      href="dist/index.html">mirrors</a> for download.</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>