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