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+\setheaders{Credits}
+\chapter*{Credits}
+%\addcontentsline{toc}{section}{Credits}
+
+{\Coq} is a proof assistant for higher-order logic, allowing the
+development of computer programs consistent with their formal
+specification. It is the result of about ten years of research of the
+Coq project. We shall briefly survey here three main aspects: the
+{\sl logical language} in which we write our axiomatizations and
+specifications, the {\sl proof assistant} which allows the development
+of verified mathematical proofs, and the {\sl program extractor} which
+synthesizes computer programs obeying their formal specifications,
+written as logical assertions in the language.
+
+The logical language used by {\Coq} is a variety of type theory,
+called the {\sl Calculus of Inductive Constructions}. Without going
+back to Leibniz and Boole, we can date the creation of what is now
+called mathematical logic to the work of Frege and Peano at the turn
+of the century. The discovery of antinomies in the free use of
+predicates or comprehension principles prompted Russell to restrict
+predicate calculus with a stratification of {\sl types}. This effort
+culminated with {\sl Principia Mathematica}, the first systematic
+attempt at a formal foundation of mathematics. A simplification of
+this system along the lines of simply typed $\lambda$-calculus
+occurred with Church's {\sl Simple Theory of Types}. The
+$\lambda$-calculus notation, originally used for expressing
+functionality, could also be used as an encoding of natural deduction
+proofs. This Curry-Howard isomorphism was used by N. de Bruijn in the
+{\sl Automath} project, the first full-scale attempt to develop and
+mechanically verify mathematical proofs. This effort culminated with
+Jutting's verification of Landau's {\sl Grundlagen} in the 1970's.
+Exploiting this Curry-Howard isomorphism, notable achievements in
+proof theory saw the emergence of two type-theoretic frameworks; the
+first one, Martin-L\"of's {\sl Intuitionistic Theory of Types},
+attempts a new foundation of mathematics on constructive principles.
+The second one, Girard's polymorphic $\lambda$-calculus $F_\omega$, is
+a very strong functional system in which we may represent higher-order
+logic proof structures. Combining both systems in a higher-order
+extension of the Automath languages, T. Coquand presented in 1985 the
+first version of the {\sl Calculus of Constructions}, CoC. This strong
+logical system allowed powerful axiomatizations, but direct inductive
+definitions were not possible, and inductive notions had to be defined
+indirectly through functional encodings, which introduced
+inefficiencies and awkwardness. The formalism was extended in 1989 by
+T. Coquand and C. Paulin with primitive inductive definitions, leading
+to the current {\sl Calculus of Inductive Constructions}. This
+extended formalism is not rigorously defined here. Rather, numerous
+concrete examples are discussed. We refer the interested reader to
+relevant research papers for more information about the formalism, its
+meta-theoretic properties, and semantics. However, it should not be
+necessary to understand this theoretical material in order to write
+specifications. It is possible to understand the Calculus of Inductive
+Constructions at a higher level, as a mixture of predicate calculus,
+inductive predicate definitions presented as typed PROLOG, and
+recursive function definitions close to the language ML.
+
+Automated theorem-proving was pioneered in the 1960's by Davis and
+Putnam in propositional calculus. A complete mechanization (in the
+sense of a semi-decision procedure) of classical first-order logic was
+proposed in 1965 by J.A. Robinson, with a single uniform inference
+rule called {\sl resolution}. Resolution relies on solving equations
+in free algebras (i.e. term structures), using the {\sl unification
+ algorithm}. Many refinements of resolution were studied in the
+1970's, but few convincing implementations were realized, except of
+course that PROLOG is in some sense issued from this effort. A less
+ambitious approach to proof development is computer-aided
+proof-checking. The most notable proof-checkers developed in the
+1970's were LCF, designed by R. Milner and his colleagues at U.
+Edinburgh, specialized in proving properties about denotational
+semantics recursion equations, and the Boyer and Moore theorem-prover,
+an automation of primitive recursion over inductive data types. While
+the Boyer-Moore theorem-prover attempted to synthesize proofs by a
+combination of automated methods, LCF constructed its proofs through
+the programming of {\sl tactics}, written in a high-level functional
+meta-language, ML.
+
+The salient feature which clearly distinguishes our proof assistant
+from say LCF or Boyer and Moore's, is its possibility to extract
+programs from the constructive contents of proofs. This computational
+interpretation of proof objects, in the tradition of Bishop's
+constructive mathematics, is based on a realizability interpretation,
+in the sense of Kleene, due to C. Paulin. The user must just mark his
+intention by separating in the logical statements the assertions
+stating the existence of a computational object from the logical
+assertions which specify its properties, but which may be considered
+as just comments in the corresponding program. Given this information,
+the system automatically extracts a functional term from a consistency
+proof of its specifications. This functional term may be in turn
+compiled into an actual computer program. This methodology of
+extracting programs from proofs is a revolutionary paradigm for
+software engineering. Program synthesis has long been a theme of
+research in artificial intelligence, pioneered by R. Waldinger. The
+Tablog system of Z. Manna and R. Waldinger allows the deductive
+synthesis of functional programs from proofs in tableau form of their
+specifications, written in a variety of first-order logic. Development
+of a systematic {\sl programming logic}, based on extensions of
+Martin-L\"of's type theory, was undertaken at Cornell U. by the Nuprl
+team, headed by R. Constable. The first actual program extractor, PX,
+was designed and implemented around 1985 by S. Hayashi from Kyoto
+University. It allows the extraction of a LISP program from a proof
+in a logical system inspired by the logical formalisms of S. Feferman.
+Interest in this methodology is growing in the theoretical computer
+science community. We can foresee the day when actual computer systems
+used in applications will contain certified modules, automatically
+generated from a consistency proof of their formal specifications. We
+are however still far from being able to use this methodology in a
+smooth interaction with the standard tools from software engineering,
+i.e. compilers, linkers, run-time systems taking advantage of special
+hardware, debuggers, and the like. We hope that {\Coq} can be of use
+to researchers interested in experimenting with this new methodology.
+
+A first implementation of CoC was started in 1984 by G. Huet and T.
+Coquand. Its implementation language was CAML, a functional
+programming language from the ML family designed at INRIA in
+Rocquencourt. The core of this system was a proof-checker for CoC seen
+as a typed $\lambda$-calculus, called the {\sl Constructive Engine}.
+This engine was operated through a high-level notation permitting the
+declaration of axioms and parameters, the definition of mathematical
+types and objects, and the explicit construction of proof objects
+encoded as $\lambda$-terms. A section mechanism, designed and
+implemented by G. Dowek, allowed hierarchical developments of
+mathematical theories. This high-level language was called the {\sl
+ Mathematical Vernacular}. Furthermore, an interactive {\sl Theorem
+ Prover} permitted the incremental construction of proof trees in a
+top-down manner, subgoaling recursively and backtracking from
+dead-alleys. The theorem prover executed tactics written in CAML, in
+the LCF fashion. A basic set of tactics was predefined, which the
+user could extend by his own specific tactics. This system (Version
+4.10) was released in 1989. Then, the system was extended to deal
+with the new calculus with inductive types by C. Paulin, with
+corresponding new tactics for proofs by induction. A new standard set
+of tactics was streamlined, and the vernacular extended for tactics
+execution. A package to compile programs extracted from proofs to
+actual computer programs in CAML or some other functional language was
+designed and implemented by B. Werner. A new user-interface, relying
+on a CAML-X interface by D. de Rauglaudre, was designed and
+implemented by A. Felty. It allowed operation of the theorem-prover
+through the manipulation of windows, menus, mouse-sensitive buttons,
+and other widgets. This system (Version 5.6) was released in 1991.
+
+Coq was ported to the new implementation Caml-light of X. Leroy and D.
+Doligez by D. de Rauglaudre (Version 5.7) in 1992. A new version of
+Coq was then coordinated by C. Murthy, with new tools designed by C.
+Parent to prove properties of ML programs (this methodology is dual to
+program extraction) and a new user-interaction loop. This system
+(Version 5.8) was released in May 1993. A Centaur interface CTCoq was
+then developed by Y. Bertot from the Croap project from
+INRIA-Sophia-Antipolis.
+
+In parallel, G. Dowek and H. Herbelin developed a new proof engine,
+allowing the general manipulation of existential variables
+consistently with dependent types in an experimental version of Coq
+(V5.9).
+
+The version V5.10 of Coq is based on a generic system for
+manipulating terms with binding operators due to Chet Murthy. A new
+proof engine allows the parallel development of partial proofs for
+independent subgoals. The structure of these proof trees is a mixed
+representation of derivation trees for the Calculus of Inductive
+Constructions with abstract syntax trees for the tactics scripts,
+allowing the navigation in a proof at various levels of details. The
+proof engine allows generic environment items managed in an
+object-oriented way. This new architecture, due to C. Murthy,
+supports several new facilities which make the system easier to extend
+and to scale up:
+
+\begin{itemize}
+\item User-programmable tactics are allowed
+\item It is possible to separately verify development modules, and to
+ load their compiled images without verifying them again - a quick
+ relocation process allows their fast loading
+\item A generic parsing scheme allows user-definable notations, with a
+ symmetric table-driven pretty-printer
+\item Syntactic definitions allow convenient abbreviations
+\item A limited facility of meta-variables allows the automatic
+ synthesis of certain type expressions, allowing generic notations
+ for e.g. equality, pairing, and existential quantification.
+\end{itemize}
+
+In the Fall of 1994, C. Paulin-Mohring replaced the structure of
+inductively defined types and families by a new structure, allowing
+the mutually recursive definitions. P. Manoury implemented a
+translation of recursive definitions into the primitive recursive
+style imposed by the internal recursion operators, in the style of the
+ProPre system. C. Mu{\~n}oz implemented a decision procedure for
+intuitionistic propositional logic, based on results of R. Dyckhoff.
+J.C. Filli{\^a}tre implemented a decision procedure for first-order
+logic without contraction, based on results of J. Ketonen and R.
+Weyhrauch. Finally C. Murthy implemented a library of inversion
+tactics, relieving the user from tedious definitions of ``inversion
+predicates''.
+
+\begin{flushright}
+Rocquencourt, Feb. 1st 1995\\
+Gérard Huet
+\end{flushright}
+
+\section*{Credits: addendum for version 6.1}
+%\addcontentsline{toc}{section}{Credits: addendum for version V6.1}
+
+The present version 6.1 of Coq is based on the V5.10 architecture. It
+was ported to the new language Objective Caml by Bruno Barras. The
+underlying framework has slightly changed and allows more conversions
+between sorts.
+
+The new version provides powerful tools for easier developments.
+
+Cristina Cornes designed an extension of the Coq syntax to allow
+definition of terms using a powerful pattern-matching analysis in the
+style of ML programs.
+
+Amokrane Saïbi wrote a mechanism to simulate
+inheritance between types families extending a proposal by Peter
+Aczel. He also developed a mechanism to automatically compute which
+arguments of a constant may be inferred by the system and consequently
+do not need to be explicitly written.
+
+Yann Coscoy designed a command which explains a proof term using
+natural language. Pierre Cr{\'e}gut built a new tactic which solves
+problems in quantifier-free Presburger Arithmetic. Both
+functionalities have been integrated to the Coq system by Hugo
+Herbelin.
+
+Samuel Boutin designed a tactic for simplification of commutative
+rings using a canonical set of rewriting rules and equality modulo
+associativity and commutativity.
+
+Finally the organisation of the \Coq\ distribution has been supervised
+by Jean-Christophe Filliâtre with the help of Judicaël Courant
+and Bruno Barras.
+
+\begin{flushright}
+Lyon, Nov. 18th 1996\\
+Christine Paulin
+\end{flushright}
+\newpage
+
+\section*{Credits: addendum for version 6.2}
+%\addcontentsline{toc}{section}{Credits: addendum for version V6.2}
+
+In version 6.2 of Coq, the parsing is done using camlp4, a
+preprocessor and pretty-printer for CAML designed by Daniel de
+Rauglaudre at INRIA. Daniel de Rauglaudre made the first adaptation
+of Coq for camlp4, this work was continued by Bruno Barras who also
+changed the structure of Coq abstract syntax trees and the primitives
+to manipulate them. The result of
+these changes is a faster parsing procedure with greatly improved
+syntax-error messages. The user-interface to introduce grammar or
+pretty-printing rules has also changed.
+
+Eduardo Giménez redesigned the internal
+tactic libraries, giving uniform names
+to Caml functions corresponding to Coq tactic names.
+
+Bruno Barras wrote new more efficient reductions functions.
+
+Hugo Herbelin introduced more uniform notations in the Coq
+specification language : the
+definitions by fixpoints and pattern-matching have a more readable
+syntax.
+Patrick Loiseleur introduced user-friendly notations for arithmetic
+expressions.
+
+New tactics were introduced: Eduardo Giménez improved a mechanism to
+introduce macros for tactics, and designed special tactics for
+(co)inductive definitions; Patrick Loiseleur designed a tactic to
+simplify polynomial expressions in an arbitrary commutative ring which
+generalizes the previous tactic implemented by Samuel Boutin.
+Jean-Christophe Filli\^atre introduced a tactic for refining a goal,
+using a proof term with holes as a proof scheme.
+
+David Delahaye designed the \textsf{SearchIsos} tool to search an
+object in the library given its type (up to isomorphism).
+
+Henri Laulhère produced the Coq distribution for the Windows environment.
+
+Finally, Hugo Herbelin was the main coordinator of the Coq documentation with
+principal contributions by Bruno Barras, David Delahaye,
+Jean-Christophe Filli\^atre, Eduardo
+Giménez, Hugo Herbelin and Patrick Loiseleur.
+
+\begin{flushright}
+Orsay, May 4th 1998\\
+Christine Paulin
+\end{flushright}
+
+% $Id$
+
+%%% Local Variables:
+%%% mode: latex
+%%% TeX-master: "Reference-Manual"
+%%% End:
+