\chapter*{Preface}

\markboth{Preface}{Preface}

This volume is a self-contained introduction to interactive proof

in higher-order logic (HOL), using the proof assistant Isabelle/HOL\@. 

Compared with existing Isabelle documentation,

it provides a direct route into higher-order logic, which most people

prefer these days. It bypasses first-order logic and minimizes

discussion of meta-theory.  It is written for potential users rather

than for our colleagues in the research world.

\index{Wenzel, Markus}%

Another departure from previous documentation is that we describe Markus

Wenzel's proof script notation instead of ML tactic scripts.  The latter

make it easier to introduce new tactics on the fly, but hardly anybody

does that.  Wenzel's dedicated syntax is elegant, replacing for example

eight simplification tactics with a single method, namely \isa{simp},

with associated options.

The book has three parts.  

\begin{itemize}

\item 

The first part, \textbf{Basic Techniques},

shows how to model functional programs in higher-order logic.  Early

examples involve lists and the natural numbers.  Most proofs

are two steps long, consisting of induction on a chosen variable

followed by the \isa{auto} tactic.  But even this elementary part

covers such advanced topics as nested and mutual recursion.

\item 

The second part, \textbf{Logic and Sets}, presents a collection of

lower-level tactics that you can use to apply rules selectively.  It

also describes Isabelle/HOL's treatment of sets, functions and

relations and explains how to define sets inductively.  One of the

examples concerns the theory of model checking, and another is drawn

from a classic textbook on formal languages.

\item 

The third part, \textbf{Advanced Material}, describes a variety of

other topics.  Among these are the real numbers, records and

overloading.  Esoteric techniques are described involving induction and

recursion.  A whole chapter is devoted to an extended example: the

verification of a security protocol.

\end{itemize}

The typesetting relies on Wenzel's theory presentation tools.  An

annotated source file is run, typesetting the theory

% and any requested Isabelle responses

in the form of a \LaTeX\ source file.  This book is derived almost entirely

from output generated in this way.  The final chapter of Part~I explains how

users may produce their own formal documents in a similar fashion.

Isabelle's \hfootref{http://isabelle.in.tum.de/}{web site} contains links to

the download area and to documentation and other information.  Most Isabelle

sessions are now run from within David Aspinall's\index{Aspinall, David}

wonderful user interface, \hfootref{http://www.proofgeneral.org/}{Proof

  General}, even together with the

\hfootref{http://www.fmi.uni-passau.de/~wedler/x-symbol/}{X-Symbol} package

for XEmacs.  This book says very little about Proof General, which has its own

documentation.  In order to run Isabelle, you will need a Standard ML

compiler.  We recommend \hfootref{http://www.polyml.org/}{Poly/ML}, which is

free and gives the best performance.  The other fully supported compiler is

\hfootref{http://cm.bell-labs.com/cm/cs/what/smlnj/index.html}{Standard ML of

  New Jersey}.

This tutorial owes a lot to the constant discussions with and the valuable

feedback from the Isabelle group at Munich: Stefan Berghofer, Olaf

M{\"u}ller, Wolfgang Naraschewski, David von Oheimb, Leonor Prensa Nieto,

Cornelia Pusch, Norbert Schirmer, Martin Strecker and Markus Wenzel. Stephan

Merz was also kind enough to read and comment on a draft version.  We

received comments from Stefano Bistarelli, Gergely Buday and Tanja

Vos.

The research has been funded by many sources, including the {\sc dfg} grants

Ni~491/2, Ni~491/3, Ni~491/4 and the {\sc epsrc} grants GR\slash K57381,

GR\slash K77051, GR\slash M75440, GR\slash R01156\slash 01 and by the

\textsc{esprit} working groups 21900 and IST-1999-29001 (the \emph{Types}

project).