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     1 \chapter*{Preface}
     2 \markboth{Preface}{Preface}   %or Preface ?
     3 \addcontentsline{toc}{chapter}{Preface} 
     5 \index{Isabelle!object-logics supported}
     7 Most theorem provers support a fixed logic, such as first-order or
     8 equational logic.  They bring sophisticated proof procedures to bear upon
     9 the conjectured formula.  An impressive example is the resolution prover
    10 Otter, which Quaife~\cite{quaife-book} has used to formalize a body of
    11 mathematics.
    13 ALF~\cite{alf}, Coq~\cite{coq} and Nuprl~\cite{constable86} each support a
    14 fixed logic too, but one far removed from first-order logic.  They are
    15 explicitly concerned with computation.  A diverse collection of logics ---
    16 type theories, process calculi, $\lambda$-calculi --- may be found in the
    17 Computer Science literature.  Such logics require proof support.  Few proof
    18 procedures exist, but the theorem prover can at least check that each
    19 inference is valid.
    21 A {\bf generic} theorem prover is one that can support many different
    22 logics.  Most of these \cite{dawson90,mural,sawamura92} work by
    23 implementing a syntactic framework that can express the features of typical
    24 inference rules.  Isabelle's distinctive feature is its representation of
    25 logics using a meta-logic.  This meta-logic is just a fragment of
    26 higher-order logic; known proof theory may be used to demonstrate that the
    27 representation is correct~\cite{paulson89}.  The representation has much in
    28 common with the Edinburgh Logical Framework~\cite{harper-jacm} and with 
    29 Felty's~\cite{felty93} use of $\lambda$Prolog to implement logics.
    31 An inference rule in Isabelle is a generalized Horn clause.  Rules are
    32 joined to make proofs by resolving such clauses.  Logical variables in
    33 goals can be instantiated incrementally.  But Isabelle is not a resolution
    34 theorem prover like Otter.  Isabelle's clauses are drawn from a richer,
    35 higher-order language and a fully automatic search would be impractical.
    36 Isabelle does not join clauses automatically, but under strict user
    37 control.  You can conduct single-step proofs, use Isabelle's built-in proof
    38 procedures, or develop new proof procedures using tactics and tacticals.
    40 Isabelle's meta-logic is higher-order, based on the typed
    41 $\lambda$-calculus.  So resolution cannot use ordinary unification, but
    42 higher-order unification~\cite{huet75}.  This complicated procedure gives
    43 Isabelle strong support for many logical formalisms involving variable
    44 binding.
    46 The diagram below illustrates some of the logics distributed with Isabelle.
    47 These include first-order logic (intuitionistic and classical), the sequent
    48 calculus, higher-order logic, Zermelo-Fraenkel set theory~\cite{suppes72},
    49 a version of Constructive Type Theory~\cite{nordstrom90}, several modal
    50 logics, and a Logic for Computable Functions.  Several experimental
    51 logics are also available, such a term assignment calculus for linear
    52 logic.  
    54 \centerline{\epsfbox{Isa-logics.eps}}
    57 \section*{How to read this book}
    58 Isabelle is a large system, but beginners can get by with a few commands
    59 and a basic knowledge of how Isabelle works.  Some knowledge of
    60 Standard~\ML{} is essential because \ML{} is Isabelle's user interface.
    61 Advanced Isabelle theorem proving can involve writing \ML{} code, possibly
    62 with Isabelle's sources at hand.  My book on~\ML{}~\cite{paulson91} covers
    63 much material connected with Isabelle, including a simple theorem prover.
    65 The Isabelle documentation is divided into three parts, which serve
    66 distinct purposes:
    67 \begin{itemize}
    68 \item {\em Introduction to Isabelle\/} describes the basic features of
    69   Isabelle.  This part is intended to be read through.  If you are
    70   impatient to get started, you might skip the first chapter, which
    71   describes Isabelle's meta-logic in some detail.  The other chapters
    72   present on-line sessions of increasing difficulty.  It also explains how
    73   to derive rules define theories, and concludes with an extended example:
    74   a Prolog interpreter.
    76 \item {\em The Isabelle Reference Manual\/} contains information about most
    77   of the facilities of Isabelle, apart from particular object-logics.  This
    78   part would make boring reading, though browsing might be useful.  Mostly
    79   you should use it to locate facts quickly.
    81 \item {\em Isabelle's Object-Logics\/} describes the various logics
    82   distributed with Isabelle.  Its final chapter explains how to define new
    83   logics.  The other chapters are intended for reference only.
    84 \end{itemize}
    85 This book should not be read from start to finish.  Instead you might read
    86 a couple of chapters from {\em Introduction to Isabelle}, then try some
    87 examples referring to the other parts, return to the {\em Introduction},
    88 and so forth.  Starred sections discuss obscure matters and may be skipped
    89 on a first reading.
    93 \section*{Releases of Isabelle}\index{Isabelle!release history}
    94 Isabelle was first distributed in 1986.  The 1987 version introduced a
    95 higher-order meta-logic with an improved treatment of quantifiers.  The
    96 1988 version added limited polymorphism and support for natural deduction.
    97 The 1989 version included a parser and pretty printer generator.  The 1992
    98 version introduced type classes, to support many-sorted and higher-order
    99 logics.  The 1993 version provides greater support for theories and is
   100 much faster.  
   102 Isabelle is still under development.  Projects under consideration include
   103 better support for inductive definitions, some means of recording proofs, a
   104 graphical user interface, and developments in the standard object-logics.
   105 I hope but cannot promise to maintain upwards compatibility.
   107 Isabelle is available by anonymous ftp:
   108 \begin{itemize}
   109 \item University of Cambridge\\
   110         host {\tt}\\
   111         directory {\tt ml}
   113 \item Technical University of Munich\\
   114         host {\tt}\\
   115         directory {\tt local/lehrstuhl/nipkow}
   116 \end{itemize}
   117 My electronic mail address is {\tt lcp\at}.  Please report any
   118 errors you find in this book and your problems or successes with Isabelle.
   121 \subsection*{Acknowledgements} 
   122 Tobias Nipkow has made immense contributions to Isabelle, including the
   123 parser generator, type classes, the simplifier, and several object-logics.
   124 He also arranged for several of his students to help.  Carsten Clasohm
   125 implemented the theory database; Markus Wenzel implemented macros; Sonia
   126 Mahjoub and Karin Nimmermann also contributed.  
   128 Nipkow and his students wrote much of the documentation underlying this
   129 book.  Nipkow wrote the first versions of \S\ref{sec:defining-theories},
   130 Chap.\ts\ref{simp-chap}, Chap.\ts\ref{Defining-Logics} and part of
   131 Chap.\ts\ref{theories}, and App.\ts\ref{app:TheorySyntax}.  Carsten Clasohm
   132 contributed to Chap.\ts\ref{theories}.  Markus Wenzel contributed to
   133 Chap.\ts\ref{Defining-Logics}.
   135 David Aspinall, Sara Kalvala, Ina Kraan, Zhenyu Qian, Norbert Voelker and
   136 Markus Wenzel suggested changes and corrections to the documentation.
   138 Martin Coen, Rajeev Gor\'e, Philippe de Groote and Philippe No\"el helped
   139 to develop Isabelle's standard object-logics.  David Aspinall performed
   140 some useful research into theories and implemented an Isabelle Emacs mode.
   141 Isabelle was developed using Dave Matthews's Standard~{\sc ml} compiler,
   142 Poly/{\sc ml}.  
   144 The research has been funded by numerous SERC grants dating from the Alvey
   145 programme (grants GR/E0355.7, GR/G53279, GR/H40570) and by ESPRIT (projects
   146 3245: Logical Frameworks and 6453: Types).
   149 \index{ML}