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-<title>Isabelle</title>
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-<h1>Isabelle </h1> <a href="http://isabelle.in.tum.de/logo/"><img
-src="isabelle.gif" width=100 align=right alt="[Isabelle logo]"></a>
-
-<p>
-
-<strong>Isabelle</strong> is a popular generic theorem proving
-environment developed at Cambridge University (<a
-href="http://www.cl.cam.ac.uk/users/lcp/">Larry Paulson</a>) and TU
-Munich (<a href="http://www.in.tum.de/~nipkow/">Tobias Nipkow</a>).
-
-<p>
-
-<a
-href="http://www.cl.cam.ac.uk/Research/HVG/Isabelle/cambridge.html"><img
-src="cambridge.gif" width=145 border=0 align=right
-alt="[Cambridge logo]"></a> <a
-href="http://isabelle.in.tum.de/munich.html"><img src="munich.gif"
-width=48 border=0 align=right alt="[Munich logo]"></a> This page
-provides general information on Isabelle, more specific information is
-available from the local pages
-
-<ul>
-
-<li> <a
-href="http://www.cl.cam.ac.uk/Research/HVG/Isabelle/cambridge.html"><strong>Isabelle
-at Cambridge</strong></a>
-
-<li> <a href="http://isabelle.in.tum.de/munich.html"><strong>Isabelle
-at Munich</strong></a>
-
-</ul>
-
-See there for information on projects done with Isabelle, mailing list
-archives, research papers, the Isabelle bibliography, and Isabelle
-workshops and courses.
-
-
-<h2>Obtaining Isabelle</h2>
-
-The current version is <strong>Isabelle99</strong>. Several mirror
-sites provide the Isabelle <a href="dist/">distribution</a>, which
-includes sources, documentation, and binary packages.
-
-
-<h2>What is Isabelle?</h2>
-
-Isabelle can be viewed from two main perspectives. On the one hand it
-may serve as a generic framework for rapid prototyping of deductive
-systems. On the other hand, major existing logics like
-<strong>Isabelle/HOL</strong> provide a theorem proving environment
-ready to use for sizable applications.
-
-
-<h3>Isabelle's Logics</h3>
-
-The Isabelle distribution includes a large body of object logics and
-other examples (see the <a href="library/">Isabelle theory
-library</a>).
-
-<dl>
-
-<dt><a href="library/HOL/"><strong>Isabelle/HOL</strong></a><dd> is a
-version of classical higher-order logic resembling that of the <A
-HREF="http://www.cl.cam.ac.uk/Research/HVG/HOL/HOL.html">HOL
-System</A>.
-
-<dt><a href="library/HOLCF/"><strong>Isabelle/HOLCF</strong></a><dd>
-adds Scott's Logic for Computable Functions (domain theory) to HOL.
-
-<dt><a href="library/FOL/"><strong>Isabelle/FOL</strong></a><dd>
-provides basic classical and intuitionistic first-order logic. It is
-polymorphic.
-
-<dt><a href="library/ZF/"><strong>Isabelle/ZF</strong></a><dd> offers
-a formulation of Zermelo-Fraenkel set theory on top of FOL.
-
-</dl>
-
-<p>
-
-Isabelle/HOL is currently the best developed object logic, including
-an extensive library of (concrete) mathematics, and various packages
-for advanced definitional concepts (like (co-)inductive sets and
-types, well-founded recursion etc.). The distribution also includes
-some large applications, for example correctness proofs of
-cryptographic protocols (<a href="library/HOL/Auth/">HOL/Auth</a>) or
-communication protocols (<a href="library/HOLCF/IOA/">HOLCF/IOA</a>).
-
-<p>
-
-Isabelle/ZF provides another starting point for applications, with a
-slightly less developed library. Its definitional packages are
-similar to those of Isabelle/HOL. Untyped ZF provides more advanced
-constructions for sets than simply-typed HOL.
-
-<p>
-
-There are a few minor object logics that may serve as further
-examples: <a href="library/CTT/">CTT</a> is an extensional version of
-Martin-Löf's Type Theory, <a href="library/Cube/">Cube</a> is
-Barendregt's Lambda Cube. There are also some sequent calculus
-examples under <a href="library/Sequents/">Sequents</a>, including
-modal and linear logics. Again see the <a href="library/">Isabelle
-theory library</a> for other examples.
-
-
-<h3>Defining Logics</h3>
-
-Logics are not hard-wired into Isabelle, but formulated within
-Isabelle's meta logic: <strong>Isabelle/Pure</strong>. There are
-quite a lot of syntactic and deductive tools available in generic
-Isabelle. Thus defining new logics or extending existing ones
-basically works as follows:
-
-<ol>
-
-<li> declare concrete syntax (via mixfix grammar and syntax macros),
-
-<li> declare abstract syntax (as higher-order constants),
-
-<li> declare inference rules (as meta-logical propositions),
-
-<li> instantiate generic automatic proof tools (simplifier, classical
-tableau prover etc.),
-
-<li> manually code special proof procedures (via tacticals or
-hand-written ML).
-
-</ol>
-
-The first three steps above are fully declarative and involve no ML
-programming at all. Thus one already gets a decent deductive
-environment based on primitive inferences (by employing the built-in
-mechanisms of Isabelle/Pure, in particular higher-order unification
-and resolution).
-
-For sizable applications some degree of automated reasoning is
-essential. Instantiating existing tools like the classical tableau
-prover involves only minimal ML-based setup. One may also write
-arbitrary proof procedures or even theory extension packages in ML,
-without breaching system soundness (Isabelle follows the well-known
-<em>LCF system approach</em> to achieve a secure system).
-
-
-<h2>Mailing list</h2>
-
-Use the mailing list <a href="mailto:
-isabelle-users@cl.cam.ac.uk">isabelle-users@cl.cam.ac.uk</a> to
-discuss problems and results.
-(Why not <A HREF="mailto:lcp@cl.cam.ac.uk">subscribe</A>?)
-
-
-</body>
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