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8 \title{Introduction to Isabelle}
9 \author{{\em Lawrence C. Paulson}\\
10 Computer Laboratory \\ University of Cambridge \\[2ex]
11 {\small{\em Electronic mail\/}: {\tt lcp@cl.cam.ac.uk}}
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34 {\small Copyright \copyright{} \number\year{} by Lawrence C. Paulson}
39 \index{Isabelle!overview}
40 \index{Isabelle!object-logics supported}
41 Isabelle~\cite{paulson86,paulson89,paulson700} is a generic theorem prover.
42 It has been instantiated to support reasoning in several object-logics:
44 \item first-order logic, constructive and classical versions
45 \item higher-order logic, similar to that of Gordon's {\sc
47 \item Zermelo-Fraenkel set theory~\cite{suppes72}
48 \item an extensional version of Martin-L\"of's Type Theory~\cite{nordstrom90}
49 \item the classical first-order sequent calculus, {\sc lk}
50 \item the modal logics $T$, $S4$, and $S43$
51 \item the Logic for Computable Functions~\cite{paulson87}
53 A logic's syntax and inference rules are specified declaratively; this
54 allows single-step proof construction. Isabelle provides control
55 structures for expressing search procedures. Isabelle also provides
56 several generic tools, such as simplifiers and classical theorem provers,
57 which can be applied to object-logics.
60 Isabelle is a large system, but beginners can get by with a small
61 repertoire of commands and a basic knowledge of how Isabelle works. Some
62 knowledge of Standard~\ML{} is essential, because \ML{} is Isabelle's user
63 interface. Advanced Isabelle theorem proving can involve writing \ML{}
64 code, possibly with Isabelle's sources at hand. My book
65 on~\ML{}~\cite{paulson91} covers much material connected with Isabelle,
66 including a simple theorem prover. Users must be familiar with logic as
67 used in computer science; there are many good
68 texts~\cite{galton90,reeves90}.
71 {\sc lcf}, developed by Robin Milner and colleagues~\cite{gordon79}, is an
72 ancestor of {\sc hol}, Nuprl, and several other systems. Isabelle borrows
73 ideas from {\sc lcf}: formulae are~\ML{} values; theorems belong to an
74 abstract type; tactics and tacticals support backward proof. But {\sc lcf}
75 represents object-level rules by functions, while Isabelle represents them
76 by terms. You may find my other writings~\cite{paulson87,paulson-handbook}
77 helpful in understanding the relationship between {\sc lcf} and Isabelle.
79 Isabelle does not keep a record of inference steps. Each step is checked
80 at run time to ensure that theorems can only be constructed by applying
81 inference rules. An Isabelle proof typically involves hundreds of
82 primitive inferences, and would be unintelligible if displayed.
83 Discarding proofs saves vast amounts of storage. But can Isabelle be
84 trusted? If desired, object-logics can be formalized such that each
85 theorem carries a proof term, which could be checked by another program.
86 Proofs can also be traced.
88 \index{Isabelle!release history} Isabelle was first distributed in 1986.
89 The 1987 version introduced a higher-order meta-logic with an improved
90 treatment of quantifiers. The 1988 version added limited polymorphism and
91 support for natural deduction. The 1989 version included a parser and
92 pretty printer generator. The 1992 version introduced type classes, to
93 support many-sorted and higher-order logics. The current version provides
94 greater support for theories and is much faster. Isabelle is still under
95 development and will continue to change.
97 \subsubsection*{Overview}
98 This manual consists of three parts. Part~I discusses the Isabelle's
99 foundations. Part~II, presents simple on-line sessions, starting with
100 forward proof. It also covers basic tactics and tacticals, and some
101 commands for invoking them. Part~III contains further examples for users
102 with a bit of experience. It explains how to derive rules define theories,
103 and concludes with an extended example: a Prolog interpreter.
105 Isabelle's Reference Manual and Object-Logics manual contain more details.
106 They assume familiarity with the concepts presented here.
109 \subsubsection*{Acknowledgements}
110 Tobias Nipkow contributed most of the section on defining theories.
111 Sara Kalvala and Markus Wenzel suggested improvements.
113 Tobias Nipkow has made immense contributions to Isabelle, including the
114 parser generator, type classes, and the simplifier. Carsten Clasohm and
115 Markus Wenzel made major contributions; Sonia Mahjoub and Karin Nimmermann
116 also helped. Isabelle was developed using Dave Matthews's Standard~{\sc
117 ml} compiler, Poly/{\sc ml}. Many people have contributed to Isabelle's
118 standard object-logics, including Martin Coen, Philippe de Groote, Philippe
119 No\"el. The research has been funded by the SERC (grants GR/G53279,
120 GR/H40570) and by ESPRIT (projects 3245: Logical Frameworks, and 6453:
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132 You can only find truth with logic\\
133 if you have already found truth without it.}\\
136 G.K. Chesterton, {\em The Man who was Orthodox}
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