-\documentclass{kluwer}
+\documentclass[draft]{kluwer}
\usepackage{color}
\usepackage{graphicx}
% \usepackage{amssymb,amsmath}
%\parpic(0cm,0cm)(#2,#3)[l]{\includegraphics[width=#1]{whelp-bw}}
%}
+\newcommand{\component}{component}
+\newcommand{\components}{components}
+
\newcommand{\AUTO}{\textsc{Auto}}
\newcommand{\COQ}{Coq}
+\newcommand{\COQIDE}{CoqIde}
\newcommand{\ELIM}{\textsc{Elim}}
+\newcommand{\GDOME}{Gdome}
\newcommand{\HELM}{Helm}
\newcommand{\HINT}{\textsc{Hint}}
\newcommand{\IN}{\ensuremath{\dN}}
\newcommand{\REF}[3]{\ensuremath{\mathit{Ref}_{#1}(#2,#3)}}
\newcommand{\TEXMACRO}[1]{\texttt{\char92 #1}}
\newcommand{\UWOBO}{UWOBO}
+\newcommand{\GETTER}{Getter}
\newcommand{\WHELP}{Whelp}
\newcommand{\DOT}{\ensuremath{\mbox{\textbf{.}}}}
\newcommand{\SEMICOLON}{\ensuremath{\mbox{\textbf{;}}}}
\definecolor{gray}{gray}{0.85} % 1 -> white; 0 -> black
\newcommand{\NT}[1]{\langle\mathit{#1}\rangle}
\newcommand{\URI}[1]{\texttt{#1}}
+\newcommand{\OP}[1]{``\texttt{#1}''}
%{\end{SaveVerbatim}\setlength{\fboxrule}{.5mm}\setlength{\fboxsep}{2mm}%
\newenvironment{grafite}{\VerbatimEnvironment
\newcommand{\NOTE}[1]{\ednote{#1}{foo}}
\newcommand{\TODO}[1]{\textbf{TODO: #1}}
+\newcounter{pass}
+\newcommand{\PASS}{\stepcounter{pass}\arabic{pass}}
+
\newsavebox{\tmpxyz}
\newcommand{\sequent}[2]{
\savebox{\tmpxyz}[0.9\linewidth]{
\institute{Department of Computer Science, University of Bologna\\
Mura Anteo Zamboni, 7 --- 40127 Bologna, ITALY}
-\runningtitle{The Matita proof assistant}
+\runningtitle{The \MATITA{} proof assistant}
\runningauthor{Asperti, Sacerdoti Coen, Tassi, Zacchiroli}
% \date{data}
\end{opening}
+
+\section{Introduction}
+\label{sec:intro}
+\MATITA{} is the Proof Assistant under development by the \HELM{} team
+\cite{mkm-helm} at the University of Bologna, under the direction of
+Prof.~Asperti. \\
+The paper describes the overall architecture of
+the system, focusing on its most distintive and innovative
+features.
+
+\subsection{Historical Perspective}
+The origins of \MATITA{} go back to 1999. At the time we were mostly
+interested to develop tools and techniques to enhance the accessibility
+via Web of formal libraries of mathematics. Due to its dimension, the
+library of the \COQ~\cite{CoqManual} proof assistant (of the order of 35'000 theorems)
+was choosed as a privileged test bench for our work, although experiments
+have been also conducted with other systems, and notably
+with \NUPRL{}\cite{nuprl-book}.
+The work, mostly performed in the framework of the recently concluded
+European project IST-33562 \MOWGLI{}~\cite{pechino}, mainly consisted in the
+following steps:
+\begin{itemize}
+\item exporting the information from the internal representation of
+ \COQ{} to a system and platform independent format. Since XML was at the
+time an emerging standard, we naturally adopted this technology, fostering
+a content-centric architecture\cite{content-centric} where the documents
+of the library were the the main components around which everything else
+has to be build;
+\item developing indexing and searching techniques supporting semantic
+ queries to the library;
+%these efforts gave birth to our \WHELP{}
+%search engine, described in~\cite{whelp};
+\item developing languages and tools for a high-quality notational
+rendering of mathematical information\footnote{We have been
+active in the MathML Working group since 1999.};
+%and developed inside
+%\HELM{} a MathML-compliant widget for the GTK graphical environment
+%which can be integrated in any application.
+\end{itemize}
+
+According to our content-centric commitment, the library exported from
+\COQ{} was conceived as being distributed and most of the tools were developed
+as Web services. The user could interact with the library and the tools by
+means of a Web interface that orchestrates the Web services.
+
+The Web services and the other tools have been implemented as front-ends
+to a set of software libraries, collectively called the \HELM{} libraries.
+At the end of the \MOWGLI{} project we already disposed of the following
+tools and software libraries:
+\begin{itemize}
+\item XML specifications for the Calculus of Inductive Constructions,
+with libraries for parsing and saving mathematical objects in such a format
+\cite{exportation-module};
+\item metadata specifications with libraries for indexing and querying the
+XML knowledge base;
+\item a proof checker library (i.e. the {\em kernel} of a proof assistant),
+implemented to check that we exported form the \COQ{} library all the
+logically relevant content;
+\item a sophisticated parser (used by the search engine), able to deal
+with potentially ambiguous and incomplete information, typical of the
+mathematical notation \cite{disambiguation};
+\item a {\em refiner} library, i.e. a type inference system, based on
+partially specified terms, used by the disambiguating parser;
+\item complex transformation algorithms for proof rendering in natural
+language \cite{remathematization};
+\item an innovative, MathML-compliant rendering widget for the GTK
+graphical environment\cite{padovani}, supporting
+high-quality bidimensional
+rendering, and semantic selection, i.e. the possibility to select semantically
+meaningful rendering expressions, and to past the respective content into
+a different text area.
+\end{itemize}
+Starting from all this, developing our own proof assistant was not
+too far away: essentially, we ``just'' had to
+add an authoring interface, and a set of functionalities for the
+overall management of the library, integrating everything into a
+single system. \MATITA{} is the result of this effort.
+
+\subsection{The System}
+DESCRIZIONE DEL SISTEMA DAL PUNTO DI VISTA ``UTENTE''
+
+\begin{itemize}
+ \item scelta del sistema fondazionale
+ \item sistema indipendente (da \COQ)
+ \item compatibilit\`a con sistemi legacy
+\end{itemize}
+
+\subsection{Relationship with \COQ{}}
+
+At first sight, \MATITA{} looks as (and partly is) a \COQ{} clone. This is
+more the effect of the circumstances of its creation described
+above than the result of a deliberate design. In particular, we
+(essentially) share the same foundational dialect of \COQ{} (the
+Calculus of (Co)Inductive Constructions), the same implementative
+language (\OCAML{}), and the same (script based) authoring philosophy.
+However, the analogy essentially stops here and no code is shared by the
+two systems.
+
+In a sense; we like to think of \MATITA{} as the way \COQ{} would
+look like if entirely rewritten from scratch: just to give an
+idea, although \MATITA{} currently supports almost all functionalities of
+\COQ{}, it links 60'000 lines of \OCAML{} code, against the 166'000 lines linked
+by \COQ{} (and we are convinced that, starting from scratch again,
+we could furtherly reduce our code in sensible way).
+
+Moreover, the complexity of the code of \MATITA{} is greatly reduced with
+respect to \COQ. For instance, the API of the libraries of \MATITA{} comprise
+989 functions, to be compared with the 4'286 functions of \COQ.
+
+Finally, \MATITA{} has several innovatives features over \COQ{} that derive
+from the integration of Mathematical Knowledge Management tools with proof
+assistants. Among them, the advanced indexing tools over the library and
+the parser for ambiguous mathematical notation.
+
+The size and complexity improvements over \COQ{} must be understood
+historically. \COQ{} is a quite old
+system whose development started 15\NOTE{Verificare} years ago. Since then
+several developers have took over the code and several new research ideas
+that were not considered in the original architecture have been experimented
+and integrated in the system. Moreover, there exists a lot of developments
+for \COQ{} that require backward compatibility between each pair of releases;
+since many central functionalities of a proof assistant are based on heuristics
+or arbitrary choices to overcome undecidability (e.g. for higher order
+unification), changing these functionalities mantaining backward compatibility
+is very difficult. Finally, the code of \COQ{} has been greatly optimized
+over the years; optimization reduces maintenability and rises the complexity
+of the code.
+
+In writing \MATITA{} we have not been hindered by backward compatibility and
+we have took advantage of the research results and experiences previously
+developed by others, comprising the authors of \COQ. Moreover, starting from
+scratch, we have designed in advance the architecture and we have splitted
+the code in coherent minimally coupled libraries.
+
+In the future we plan to exploit \MATITA{} as a test bench for new ideas and
+extensions. Keeping the single libraries and the whole architecture as
+simple as possible is thus crucial to foster future experiments and to
+allow other developers to quickly understand our code and contribute.
+
+%For direct experience of the authors, the learning curve to understand and
+%be able to contribute to \COQ{}'s code is quite steep and requires direct
+%and frequent interactions with \COQ{} developers.
+
\begin{figure}[t]
\begin{center}
- \includegraphics[width=0.9\textwidth]{libraries}
+ \includegraphics[width=0.9\textwidth]{librariesCluster.ps}
\caption{\MATITA{} libraries}
+ \label{fig:libraries}
\end{center}
- \label{fig:libraries}
\end{figure}
-\section{Overview of the Architecture}
-Fig.~\ref{fig:libraries} shows the architecture of the \emph{libraries} (circle nodes)
-and \emph{applications} (squared nodes) developed in the HELM project.
+\section{Architecture}
+\label{architettura}
+Fig.~\ref{fig:libraries} shows the architecture of the \emph{\components}
+(circle nodes) and \emph{applications} (squared nodes) developed in the HELM
+project.
-Applications and libraries depend over other libraries forming a
-directed acyclic graph (DAG). Each library can be decomposed in
+Applications and \components{} depend over other \components{} forming a
+directed acyclic graph (DAG). Each \component{} can be decomposed in
a a set of \emph{modules} also forming a DAG.
-Modules and libraries provide coherent sets of functionalities
+Modules and \components{} provide coherent sets of functionalities
at different scales. Applications that require only a few functionalities
-depend on a restricted set of libraries. \MATITA, our most complex
-application, depends on every library.
+depend on a restricted set of \components{}.
-Only the proof assistant \MATITA{} is an application meant to be used directly
-by the user. All the other applications are Web services developed in the
-HELM and MoWGLI projects and already described elsewhere. In particular:
+Only the proof assistant \MATITA{} and the \WHELP{} search engine are
+applications meant to be used directly by the user. All the other applications
+are Web services developed in the HELM and MoWGLI projects and already described
+elsewhere. In particular:
\begin{itemize}
\item The \emph{Getter} is a Web service to retrieve an (XML) document
from a physical location (URL) given its logical name (URI). The Getter is
responsible of updating a table that maps URIs to URLs. Thanks to the Getter
it is possible to work on a logically monolithic library that is physically
distributed on the network. More information on the Getter can be found
- in~\cite{getter}.
+ in~\cite{zack-master}.
\item \emph{Whelp} is a search engine to index and locate mathematical
notions (axioms, theorems, definitions) in the logical library managed
by the Getter. Typical examples of a query to Whelp are queries that search
two dimensional mathematical notation. Uwobo may also embed the rendering
of mathematical notions into arbitrary documents before returning them.
The Getter is used by Uwobo to retrieve the document to be rendered.
- Uwobo has been described in~\cite{uwobo}.
+ Uwobo has been described in~\cite{zack-master}.
\item The \emph{Proof Checker} is a Web service that, given the URI of
notion in the distributed library, checks its correctness. Since the notion
is likely to depend in an acyclic way over other notions, the proof checker
is also responsible of building in a top-down way the DAG of all
dependencies, checking in turn every notion for correctness.
- The proof checker has been described in~\cite{proofchecker}.
+ The proof checker has been described in~\cite{zack-master}.
\item The \emph{Dependency Analyzer} is a Web service that can produce
a textual or graphical representation of the dependecies of an object.
- The dependency analyzer has been described in~\cite{dependencyanalyzer}.
+ The dependency analyzer has been described in~\cite{zack-master}.
\end{itemize}
-The dependency of a library or application over another library can
-be satisfied by linking the library in the same executable.
-For those libraries whose functionalities are also provided by the
+The dependency of a \component{} or application over another \component{} can
+be satisfied by linking the \component{} in the same executable.
+For those \components{} whose functionalities are also provided by the
aforementioned Web services, it is also possible to link stub code that
forwards the request to a remote Web service. For instance, the Getter
-is just a wrapper to the \texttt{getter} library that allows the library
-to be used as a Web service. \MATITA{} can directly link the code of the
-\texttt{getter} library, or it can use a stub library with the same API
-that forwards every request to the Getter.
+is just a wrapper to the \GETTER \component{} that allows the
+\component{} to be used as a Web service. \MATITA{} can directly link the code
+of the \GETTER \component, or it can use a stub library with the same
+API that forwards every request to the Getter.
To better understand the architecture of \MATITA{} and the role of each
-library, we can focus on the rappresentation of the mathematical information.
+\component, we can focus on the representation of the mathematical information.
\MATITA{} is based on (a variant of) the Calculus of (Co)Inductive
Constructions (CIC). In CIC terms are used to represent mathematical
expressions, types and proofs. \MATITA{} is able to handle terms at
-four different levels of refinement. On each level it is possible to provide a
-different set of functionalities. The four different levels are:
-fully specified terms; partially specified terms; terms
-at the content level; terms at the presentation level.
+four different levels of specification. On each level it is possible to provide
+a different set of functionalities. The four different levels are:
+fully specified terms; partially specified terms;
+content level terms; presentation level terms.
\subsection{Fully specified terms}
+\label{fully-spec}
\emph{Fully specified terms} are CIC terms where no information is
missing or left implicit. A fully specified term should be well-typed.
The mathematical notions (axioms, definitions, theorems) that are stored
extendible mathematical notation. They are not meant for direct user
consumption.
- The \texttt{cic} library defines the data type that represents CIC terms
+ The \texttt{cic} \component{} defines the data type that represents CIC terms
and provides a parser for terms stored in an XML format.
- The most important library that deals with fully specified terms is
+ The most important \component{} that deals with fully specified terms is
\texttt{cic\_proof\_checking}. It implements the procedure that verifies
if a fully specified term is well-typed. It also implements the
\emph{conversion} judgement that verifies if two given terms are
Terms may reference other mathematical notions in the library.
One commitment of our project is that the library should be physically
- distributed. The \texttt{getter} library manages the distribution,
+ distributed. The \GETTER \component{} manages the distribution,
providing a mapping from logical names (URIs) to the physical location
- of a notion (an URL). The \texttt{urimanager} library provides the URI
+ of a notion (an URL). The \texttt{urimanager} \component{} provides the URI
data type and several utility functions over URIs. The
- \texttt{cic\_proof\_checking} library calls the \texttt{getter} library
- every time it needs to retrieve the definition of a mathematical notion
- referenced by a term that is being type-checked.
+ \texttt{cic\_proof\_checking} \component{} calls the \GETTER
+ \component{} every time it needs to retrieve the definition of a mathematical
+ notion referenced by a term that is being type-checked.
- The Proof Checker is the Web service that provides an HTTP interface
- to the \texttt{cic\_proof\_checking} library.
+ The Proof Checker is the Web service that provides an interface
+ to the \texttt{cic\_proof\_checking} \component.
We use metadata and a sort of crawler to index the mathematical notions
in the distributed library. We are interested in retrieving a notion
by matching, instantiation or generalization of a user or system provided
mathematical expression. Thus we need to collect metadata over the fully
specified terms and to store the metadata in some kind of (relational)
- database for later usage. The \texttt{hmysql} library provides a simplified
+ database for later usage. The \texttt{hmysql} \component{} provides
+ a simplified
interface to a (possibly remote) MySql database system used to store the
- metadata. The \texttt{metadata} library defines the data type of the metadata
+ metadata. The \texttt{metadata} \component{} defines the data type of the
+ metadata
we are collecting and the functions that extracts the metadata from the
mathematical notions (the main functionality of the crawler).
- The \texttt{whelp} library implements a search engine that performs
+ The \texttt{whelp} \component{} implements a search engine that performs
approximated queries by matching/instantiation/generalization. The queries
operate only on the metadata and do not involve any actual matching
(that will be described later on and that is implemented in the
- \texttt{cic\_unification} library). Not performing any actual matching
+ \texttt{cic\_unification} \component). Not performing any actual matching
the query only returns a complete and hopefully small set of matching
candidates. The process that has issued the query is responsible of
actually retrieving from the distributed library the candidates to prune
out false matches if interested in doing so.
The Whelp search engine is the Web service that provides an interface to
- the \texttt{whelp} library.
-
+ the \texttt{whelp} \component.
+
+ According to our vision, the library is developed collaboratively so that
+ changing or removing a notion can invalidate other notions in the library.
+ Moreover, changing or removing a notion requires a corresponding change
+ in the metadata database. The \texttt{library} \component{} is responsible
+ of preserving the coherence of the library and the database. For instance,
+ when a notion is removed, all the notions that depend on it and their
+ metadata are removed from the library. This aspect will be better detailed
+ in Sect.~\ref{sec:libmanagement}.
+
\subsection{Partially specified terms}
\emph{Partially specified terms} are CIC terms where subterms can be omitted.
Omitted subterms can bear no information at all or they may be associated to
a type-inference procedure that can instantiate implicit terms and
metavariables and that can introduce \emph{implicit coercions} to make a
partially specified term be well-typed. The refiner of \MATITA{} is implemented
-in the \texttt{cic\_unification} library. As the type checker is based on
+in the \texttt{cic\_unification} \component. As the type checker is based on
the conversion check, the refiner is based on \emph{unification} that is
a procedure that makes two partially specified term convertible by instantiating
as few as possible metavariables that occur in them.
-Since terms are use in CIC to represent proofs, so far correct incomplete
+Since terms are used in CIC to represent proofs, correct incomplete
proofs are represented by refinable partially specified terms. The metavariables
that occur in the proof correspond to the conjectures still to be proved.
The sequent associated to the metavariable is the conjecture the user needs to
\emph{Tactics} are the procedures that the user can apply to progress in the
proof. A tactic proves a conjecture possibly creating new (and hopefully
simpler) conjectures. The implementation of tactics is given in the
-\texttt{tactics} library. It is heavily based on the refinement and unification
-procedures of the \texttt{cic\_unification} library.
+\texttt{tactics} \component. It is heavily based on the refinement and
+unification procedures of the \texttt{cic\_unification} \component.
+
+The \texttt{grafite} \component{} defines the abstract syntax tree (AST) for the
+commands of the \MATITA{} proof assistant. Most of the commands are tactics.
+Other commands are used to give definitions and axioms or to state theorems
+and lemmas. The \texttt{grafite\_engine} \component{} is the core of \MATITA{}.
+It implements the semantics of each command in the grafite AST as a function
+from status to status. It implements also an undo function to go back to
+previous statuses. \TODO{parlare di disambiguazione lazy \& co?}
As fully specified terms, partially specified terms are not well suited
for user consumption since their syntax is not extendible and it is not
an improvement over fully specified terms since they allow to omit redundant
information that can be inferred by the refiner.
-\subsection{Terms at the content level}
+\subsection{Content level terms}
+\label{sec:contentintro}
+
The language used to communicate proofs and expecially expressions with the
user does not only needs to be extendible and accomodate the usual mathematical
notation. It must also reflect the comfortable degree of imprecision and
For instance, it is common practice in mathematics to speak of a generic
equality that can be used to compare any two terms. However, it is well known
-that several equalities can be identified as soon as we care for decidability
+that several equalities can be distinguished as soon as we care for decidability
or for their computational properties. For instance equality over real
numbers is well known to be undecidable, whereas it is decidable over
rational numbers.
Mathematical Knowledge Management community this imprecise language is called
the \emph{content level} representation of expressions.
-In \MATITA{} we provide two translations from partially refined terms
+In \MATITA{} we provide two translations: from partially specified terms
to content level terms and the other way around. The first translation can also
-be applied to fully refined terms since a fully refined term is a special case
-of partially refined term where no metavariable or implicit term occurs.
+be applied to fully specified terms since a fully specified term is a special
+case of partially specified term where no metavariable or implicit term occurs.
-The translation from partially refined terms to content level terms must
+The translation from partially specified terms to content level terms must
discriminate between terms used to represent proofs and terms used to represent
expressions. The firsts are translated to a content level representation of
-proofs steps that can easily be rendered in natural language. The latters
-are translated to MathML Content formulae. MathML Content is a W3C standard
+proof steps that can easily be rendered in natural language. The latters
+are translated to MathML Content formulae. MathML Content~\cite{mathml} is a W3C
+standard
for the representation of content level expressions in an XML extensible format.
The translation to content level is implemented in the
-\texttt{acic\_to\_content} library. Its input are \emph{annotated partially
-refined terms}. Annotated partially refined terms are maximally unshared
-partially refined terms enriched with additional typing information for each
+\texttt{acic\_content} \component. Its input are \emph{annotated partially
+specified terms}, that are maximally unshared
+partially specified terms enriched with additional typing information for each
subterm. This information is used to discriminate between terms that represent
proofs and terms that represent expressions. Part of it is also stored at the
content level since it is required to generate the natural language rendering
-of proofs. The \emph{cic\_to\_acic} library annotates partially refined terms.
+of proofs. The terms need to be maximally unshared (i.e. they must be a tree
+and not a DAG). The reason is that to the occurrences of a subterm in
+two different positions we need to associate different typing informations.
+This association is made easier when the term is represented as a tree since
+it is possible to label each node with an unique identifier and associate
+the typing information using a map on the identifiers.
+The \texttt{cic\_acic} \component{} unshares and annotates terms. It is used
+by the \texttt{library} \component{} since fully specified terms are stored
+in the library in their annotated form.
+
+We do not provide yet a reverse translation from content level proofs to
+partially specified terms. But in \texttt{cic\_disambiguation} we do provide
+the reverse translation for expressions. The mapping from
+content level expressions to partially specified terms is not unique due to
+the ambiguity of the content level. As a consequence the translation
+is guided by an \emph{interpretation}, that is a function that chooses for
+every ambiguous expression one partially specified term. The
+\texttt{cic\_disambiguation} \component{} implements the
+disambiguation algorithm we presented in~\cite{disambiguation} that is
+responsible of building in an efficicent way the set of all ``correct''
+interpretations. An interpretation is correct if the partially specified term
+obtained using the interpretation is refinable.
+
+\subsection{Presentation level terms}
+
+Content level terms are a sort of abstract syntax trees for mathematical
+expressions and proofs. The concrete syntax given to these abstract trees
+is called \emph{presentation level}.
+
+The main important difference between the content level language and the
+presentation level language is that only the former is extendible. Indeed,
+the presentation level language is a finite language that comprises all
+the usual mathematical symbols. Mathematicians invent new notions every
+single day, but they stick to a set of symbols that is more or less fixed.
+
+The fact that the presentation language is finite allows the definition of
+standard languages. In particular, for formulae we have adopt MathML
+Presentation~\cite{mathml} that is an XML dialect standardized by the W3C. To
+visually
+represent proofs it is enough to embed formulae in plain text enriched with
+formatting boxes. Since the language of formatting boxes is very simple,
+many equivalent specifications exist and we have adopted our own, called
+BoxML.
+
+The \texttt{content\_pres} \component{} contains the implementation of the
+translation from content level terms to presentation level terms. The
+rendering of presentation level terms is left to the application that uses
+the \component. However, in the \texttt{hgdome} \component{} we provide a few
+utility functions to build a \GDOME~\cite{gdome2} MathML+BoxML tree from our
+presentation
+level terms. \GDOME{} MathML+BoxML trees can be rendered by the GtkMathView
+widget developed by Luca Padovani \cite{padovani}. The widget is
+particularly interesting since it allows to implement \emph{semantic
+selection}.
+
+Semantic selection is a technique that consists in enriching the presentation
+level terms with pointers to the content level terms and to the partially
+specified terms they correspond to. Highlight of formulae in the widget is
+constrained to selection of meaningful expressions, i.e. expressions that
+correspond to a lower level term, that is a content term or a partially or
+fully specified term.
+Once the rendering of a lower level term is
+selected it is possible for the application to retrieve the pointer to the
+lower level term. An example of applications of semantic selection is
+\emph{semantic cut\&paste}: the user can select an expression and paste it
+elsewhere preserving its semantics (i.e. the partially specified term),
+possibly performing some semantic transformation over it (e.g. renaming
+variables that would be captured or lambda-lifting free variables).
+
+The reverse translation from presentation level terms to content level terms
+is implemented by a parser that is also found in \texttt{content\_pres}.
+Differently from the translation from content level terms to partially
+refined terms, this translation is not ambiguous. The reason is that the
+parsing tool we have adopted (CamlP4) is not able to parse ambiguous
+grammars. Thus we require the mapping from presentation level terms
+(concrete syntax) to content level terms (abstract syntax) to be unique.
+This means that the user must fix once and for all the associativity and
+precedence level of every operator he is using. In practice this limitation
+does not seem too strong. The reason is that the target of the
+translation is an ambiguous language and the user is free to associate
+to every content level term several different interpretations (as a
+partially specified term).
+
+Both the direct and reverse translation from presentation to content level
+terms are parameterized over the user provided mathematical notation.
+The \texttt{lexicon} \component{} is responsible of managing the lexicon,
+that is the set of active notations. It defines an abstract syntax tree
+of commands to declare and activate new notations and it implements the
+semantics of these commands. It also implements undoing of the semantic
+actions. Among the commands there are hints to the
+disambiguation algorithm that are used to control and speed up disambiguation.
+These mechanisms will be further discussed in Sect.~\ref{sec:disambiguation}.
+
+Finally, the \texttt{grafite\_parser} \component{} implements a parser for
+the concrete syntax of the commands of \MATITA. The parser process a stream
+of characters and returns a stream of abstract syntax trees (the ones
+defined by the \texttt{grafite} component and whose semantics is given
+by \texttt{grafite\_engine}). When the parser meets a command that changes
+the lexicon, it invokes the \texttt{lexicon} \component{} to immediately
+process the command. When the parser needs to parse a term at the presentation
+level, it invokes the already described parser for terms contained in
+\texttt{content\_pres}.
+
+The \MATITA{} proof assistant and the \WHELP{} search engine are both linked
+against the \texttt{grafite\_parser} \components{}
+since they provide an interface to the user. In both cases the formulae
+written by the user are parsed using the \texttt{content\_pres} \component{} and
+then disambiguated using the \texttt{cic\_disambiguation} \component.
+However, only \MATITA{} is linked against the \texttt{grafite\_engine} and
+\texttt{tactics} components since \WHELP{} can only execute those ASTs that
+correspond to queries (implemented in the \texttt{whelp} component).
+
+The \UWOBO{} Web service wraps the \texttt{content\_pres} \component,
+providing a rendering service for the documents in the distributed library.
+To render a document given its URI, \UWOBO{} retrieves it using the
+\GETTER{} obtaining a document with fully specified terms. Then it translates
+it to the presentation level passing through the content level. Finally
+it returns the result document to be rendered by the user's
+browser.\footnote{\TODO{manca la passata verso HTML}}
+
+
+The \components{} not yet described (\texttt{extlib}, \texttt{xml},
+\texttt{logger}, \texttt{registry} and \texttt{utf8\_macros}) are
+minor \components{} that provide a core of useful functions and basic
+services missing from the standard library of the programming language.
+In particular, the \texttt{xml} \component{} is used
+to easily represent, parse and pretty-print XML files.
+
+\section{Using \MATITA (boh \ldots cambiare titolo)}
-The translation from content level terms to partially refined terms is
-also performed in \ldots ???
+\begin{figure}[t]
+ \begin{center}
+% \includegraphics[width=0.9\textwidth]{a.eps}
+ \caption{\MATITA{} screenshot}
+ \label{fig:screenshot}
+ \end{center}
+\end{figure}
-\subsection{Terms at the presentation level}
+\MATITA{} has a script based user interface. As can be seen in Fig.~... it is
+split in two main windows: on the left a textual widget is used to edit the
+script, on the right the list of open goal is shown using a MathML rendering
+widget. A distinguished part of the script (shaded in the screenshot) represent
+the commands already executed and can't be edited without undoing them. The
+remaining part can be freely edited and commands from that part can be executed
+moving down the execution point. An additional window --- the ``cicBrowser'' ---
+can be used to browse the library, including the proof being developed, and
+enable content based search on it. In the cicBrowser proofs are rendered in
+natural language, automatically generated from the low-level $\lambda$-terms
+using techniques inspired by \cite{natural,YANNTHESIS}.
+
+In the \MATITA{} philosophy the script is not relevant \emph{per se}, but is
+only seen as a convenient way to create mathematical objects. The universe of
+all these objects makes up the \HELM{} library, which is always completely
+visible to the user. The mathematical library is thus conceived as a global
+hypertext, where objects may freely reference each other. It is a duty of
+the system to guide the user through the relevant parts of the library.
+
+This methodological assumption has many important consequences
+which will be discussed in the next section.
+
+%on one side
+%it requires functionalities for the overall management of the library,
+%%%%%comprising efficient indexing techniques to retrieve and filter the
+%information;
+%on the other it introduces overloading in the use of
+%identifiers and mathematical notation, requiring sophisticated disambiguation
+%techniques for interpreting the user inputs.
+%In the next two sections we shall separately discuss the two previous
+%points.
+
+%In order to maximize accessibility mathematical objects are encoded in XML. (As%discussed in the introduction,) the modular architecture of \MATITA{} is
+%organized in components which work on data in this format. For instance the
+%rendering engine, which transform $\lambda$-terms encoded as XML document to
+%MathML Presentation documents, can be used apart from \MATITA{} to print ...
+%FINIRE
+
+A final section is devoted to some innovative aspects
+of the authoring system, such as a step by step tactical execution,
+content selection and copy-paste.
+
+\section{Library Management}
+
+\subsection{Indexing and searching}
+
+
+\subsection{Compilation and decompilation}
+\label{sec:libmanagement}
+
+The aim of this section is to describe the way matita
+preserves the consistency and the availability of the library
+trough the \WHELP{} technology, in response to the user addition or
+deletion of mathematical objects.
+
+As already sketched in \ref{fully-spec} the output of the
+compilation of a script is split among two storage media, a
+classical filesystem and a relational database. The former is used to
+store the XML encoding of the objects defined in the script, the
+disambiguation aliases and the interpretation and notational convention defined,
+while the latter is used to store all the metadata needed by
+\WHELP{}. In addition the \GETTER component
+should be updated with the the new mapping between the logical URI
+and the physical path of objects.
+
+While this kind of consistency has nothing to do with the nature of
+the content of the library and is thus of poor interest (but really
+tedious to implement and keep bug-free), there is a more deep
+notion of mathematical consistency we need to provide. Each object
+must reference only defined object (i.e. each proof must use only
+already proved theorems).
+
+We will focus on how matita ensures the interesting kind
+of consistency during the formalization of a mathematical theory,
+giving the user the freedom of adding, deleting, modifying objects
+without loosing the feeling of an always visible and browsable
+library.
+
+\subsubsection{Compilation}
+The typechecker component guarantees that if an object is well typed
+it depends only on well defined objects available in the library,
+that is exactly what we need to be sure that the logic consistency of
+the library is preserved. We have only find the right order of
+compilation of the scripts that compose the user development.
+
+For this purpose we developed a low level tool called \emph{matitadep}
+that takes in input the list of files that compose the development and
+outputs their dependencies in a format suitable for the make utility.
+The user is not asked to run \emph{matitadep} nor make by hand, but
+simply to tell matita the root directory of his development (where all
+script files can be found) and matita will handle all the compilation
+tasks.\\
+To calculate dependencies it is enough to look at the script file for
+its inclusions of other parts of the development or for explicit
+references to other objects (i.e. with explicit aliases, see
+\ref{aliases}).
+
+The output of the compilation is immediately available to the user
+trough the \WHELP{} technology, since all metadata are stored in a
+user-specific area of the database where the search engine has read
+access, and all the automated tactics that operates on the whole
+library, like auto, have full visibility of the newly defined objects.
+
+Compilation is rather simple, and the only tricky case is when we want
+to compile again the same script, maybe after the deletion of a
+theorem. Here the policy is simple: decompile it before recompiling.
+As we will see in the next section decompilation will ensure that
+there will be no theorems in the development that depends on the
+removed item.
+
+\subsubsection{Decompilation}
+Decompiling an object involves,
+recursively, the decompilation of all the objects that depend on it.
+
+The calculation of the reverse dependencies can be computed in two
+ways, using the relational database or using a simpler set of metadata
+that matita saves in the filesystem as a result of compilation. The
+former technique is the same used by the \emph{Dependency Analyzer}
+described in \cite{zack-master} and really depends on a relational
+database.\\
+The latter is a fall-back in case the database is not available. Due to
+the complex deployment of a complex peace of software like a database,
+it is a common usage for the \HELM{} team to use a single and remote
+database, that may result unavailable if the user workstation lacks
+connectivity. This facility has to be intended only as a fall-back,
+since the whole \WHELP{} technology depends on the database.
+
+Decompilation guarantees that if an object is removed there are no
+dandling references to it, and that the part of the library still
+compiled is logically consistent. Since decompilation involves the
+deletion of all the outputs of the compilation, metadata included, the
+library browsable trough the \WHELP{} technology is always up to date.
+
+\subsubsection{Interactive and batch (de)compilation}
+\MATITA{} includes an interactive graphical interface and a batch
+compiler. Only the former is intended to be used directly by the
+user, the latter is automatically invoked when a not yet compiled
+part of the user development is required.
+
+While they share the same engine for compilation and decompilation,
+they provide different granularity. The batch compiler is only able to
+compile a whole script file and reciprocally it can decompile only a whole
+script, and consequently all the other scripts that rely on an object
+defined in it. The interactive interface is able to execute single steps
+of compilation, that may include the definition of an object, and
+symmetrically to undo single steps, thus removing single objects.
+
+%
+%goals: consentire sviluppo di una librearia mantenendo integrita' referenziale e usando le teconologie nostre (quindi con metadati, XML, libreria visibile)
+%\subsubsection{Composition}
+%scripts.ma, .moo, XML, metadata
+%\subsubsection{Compilation}
+%analogie con compilazione classica dso.\\
+%granularita' differenti per uso interattivo e non
+%\paragraph{Batch}
+%- granularita' .ma/buri \\
+%-- motivazioni\\
+%- come si calcolano le dipendenze\\
+%- quando la si usa\\
+%- metodi (cc e clean)\\
+%- garanzie
+%\paragraph{Interactive}
+%- granularita' fine\\
+%-- motivazioni
+%\label{sec:libmanagement}
+%consistenza: integrita' referenziale
+%Goals: mantenere consistente la rappresentazione della libreria su memoria persistente consentendo di compilare e decompilare le compilation unit (.ma).\\
+%Vincoli: dipendenze oggetti-oggetti e metadati-oggetti\\
+%Due livelli di gestione libreria, uno e' solo in fase interattiva dove la compilazione e' passo passo: \\
+%--- granularita' oggetto per matita interactive\\
+%--- granularita' baseuri (compilation unit) per la libreria\\
+%In entrmbi i casi ora:\\
+%--- matitaSync: add, remove, timetravel(facility-macro tra 2 stati)[obj]\\
+%--- matitaCleanLib: clean\_baseuri (che poi usa matitaSync a sua volta)[comp1]\\
+%Vincoli di add: typecheck ( ==$>$ tutto quello che usa sta in lib)\\
+%Vincoli di remove: \\
+%--- la remove di mSync non li controlla (ma sa cosa cancellare per ogni uri)\\
+%--- la clean\_baseuri calcola le dipendenze con i metadati (o anche i moo direi) e li rispetta\\
+%Undo di matita garantisce la consistenza a patto che l'history che tiene sia ok\\
+%Undo della lib (mClean) garantisce la consistenza (usando moo o Db).\\
+
+\subsection{Automation}
+
+\subsection{\MATITA's naming convention}
+A minor but not entirely negligible aspect of \MATITA{} is that of
+adopting a (semi)-rigid naming convention for identifiers, derived by
+our studies about metadata for statements.
+The convention is only applied to identifiers for theorems
+(not definitions), and relates the name of a proof to its statement.
+The basic rules are the following:
+\begin{itemize}
+\item each identifier is composed by an ordered list of (short)
+names occurring in a left to right traversal of the statement;
+\item all identifiers should (but this is not strictly compulsory)
+separated by an underscore,
+\item identifiers in two different hypothesis, or in an hypothesis
+and in the conlcusion must be separated by the string ``\verb+_to_+'';
+\item the identifier may be followed by a numerical suffix, or a
+single or duoble apostrophe.
-\hrule
+\end{itemize}
+Take for instance the theorem
+\[\forall n:nat. n = plus \; n\; O\]
+Possible legal names are: \verb+plus_n_O+, \verb+plus_O+,
+\verb+eq_n_plus_n_O+ and so on.
+Similarly, consider the theorem
+\[\forall n,m:nat. n<m \to n \leq m\]
+In this case \verb+lt_to_le+ is a legal name,
+while \verb+lt_le+ is not.\\
+But what about, say, the symmetric law of equality? Probably you would like
+to name such a theorem with something explicitly recalling symmetry.
+The correct approach,
+in this case, is the following. You should start with defining the
+symmetric property for relations
+
+\[definition\;symmetric\;= \lambda A:Type.\lambda R.\forall x,y:A.R x y \to R y x \]
+
+Then, you may state the symmetry of equality as
+\[ \forall A:Type. symmetric \;A\;(eq \; A)\]
+and \verb+symmetric_eq+ is valid \MATITA{} name for such a theorem.
+So, somehow unexpectedly, the introduction of semi-rigid naming convention
+has an important benefical effect on the global organization of the library,
+forcing the user to define abstract notions and properties before
+using them (and formalizing such use).
+
+Two cases have a special treatment. The first one concerns theorems whose
+conclusion is a (universally quantified) predicate variable, i.e.
+theorems of the shape
+$\forall P,\dots.P(t)$.
+In this case you may replace the conclusion with the word
+``elim'' or ``case''.
+For instance the name \verb+nat_elim2+ is a legal name for the double
+induction principle.
+
+The other special case is that of statements whose conclusion is a
+match expression.
+A typical example is the following
+\begin{verbatim}
+ \forall n,m:nat.
+ match (eqb n m) with
+ [ true \Rightarrow n = m
+ | false \Rightarrow n \neq m]
+\end{verbatim}
+where $eqb$ is boolean equality.
+In this cases, the name can be build starting from the matched
+expression and the suffix \verb+_to_Prop+. In the above example,
+\verb+eqb_to_Prop+ is accepted.
+
+\section{The \MATITA{} user interface}
+
+\subsection{Disambiguation}
+\label{sec:disambiguation}
+
+Software applications that involve input of mathematical content should strive
+to require the user as less drift from informal mathematics as possible. We
+believe this to be a fundamental aspect of such applications user interfaces.
+Being that drift in general very large when inputing
+proofs~\cite{debrujinfactor}, in \MATITA{} we achieved good results for
+mathematical formulae which can be input using a \TeX-like encoding (the
+concrete syntax corresponding to presentation level terms) and are then
+translated (in multiple steps) to partially specified terms as sketched in
+Sect.~\ref{sec:contentintro}.
+
+The key component of the translation is the generic disambiguation algorithm
+implemented in the \texttt{disambiguation} component of Fig.~\ref{fig:libraries}
+and presented in~\cite{disambiguation}. In this section we present how to use
+such an algorithm in the context of the development of a library of formalized
+mathematics. We will see that using multiple passes of the algorithm, varying
+some of its parameters, helps in keeping the input terse without sacrificing
+expressiveness.
+
+\subsubsection{Disambiguation aliases}
+\label{aliases}
+Let's start with the definition of the ``strictly greater then'' notion over
+(Peano) natural numbers.
+
+\begin{grafite}
+include "nat/nat.ma".
+..
+definition gt: nat \to nat \to Prop \def
+ \lambda n, m. m < n.
+\end{grafite}
-At the bottom of the DAG we have a few libraries (\texttt{extlib},
-\texttt{xml} and the \texttt{registry}) that provide a core of
-useful functions used everywhere else. In particular, the \texttt{xml} library
-to easily represent, parse and pretty-print XML files is a central component
-since in HELM every piece of information is stored in \ldots. [FINIRE]
-The other basic libraries provide often needed operations over generic
-data structures (\texttt{extlib}) and central storage for configuration options
-(the \texttt{registry}).
+The \texttt{include} statement adds the requirement that the part of the library
+defining the notion of natural numbers should be defined before
+processing the what follows. Note indeed that the algorithm presented
+in~\cite{disambiguation} does not describe where interpretations for ambiguous
+expressions come from, since it is application-specific. As a first
+approximation, we will assume that in \MATITA{} they come from the library (i.e.
+all interpretations available in the library are used) and the \texttt{include}
+statements are used to ensure the availability of required library slices (see
+Sect.~\ref{sec:libmanagement}).
+
+While processing the \texttt{gt} definition, \MATITA{} has to disambiguate two
+terms: its type and its body. Being available in the required library only one
+interpretation both for the unbound identifier \texttt{nat} and for the
+\OP{<} operator, and being the resulting partially specified term refinable,
+both type and body are easily disambiguated.
+
+Now suppose we have defined integers as signed natural numbers, and that we want
+to prove a theorem about an order relationship already defined on them (which of
+course overload the \OP{<} operator):
-\texttt{urimanager}
+\begin{grafite}
+include "Z/z.ma".
+..
+theorem Zlt_compat:
+ \forall x, y, z. x < y \to y < z \to x < z.
+\end{grafite}
+
+Since integers are defined on top of natural numbers, the part of the library
+concerning the latters is available when disambiguating \texttt{Zlt\_compat}'s
+type. Thus, according to the disambiguation algorithm, two different partially
+specified terms could be associated to it. At first, this might not be seen as a
+problem, since the user is asked and can choose interactively which of the two
+she had in mind. However in the long run it has the drawbacks of inhibiting
+batch compilation of the library (a technique used in \MATITA{} for behind the
+scene compilation when needed, e.g. when an \texttt{include} is issued) and
+yields to poor user interaction (imagine how tedious would be to be asked for a
+choice each time you re-evaluate \texttt{Zlt\_compat}!).
+
+For this reason we added to \MATITA{} the concept of \emph{disambiguation
+aliases}. Disambiguation aliases are one-to-many mappings from ambiguous
+expressions to partially specified terms, which are part of the runtime status
+of \MATITA. They can be provided by users with the \texttt{alias} statement, but
+are usually automatically added when evaluating \texttt{include} statements
+(\emph{implicit aliases}). Aliases implicitely inferred during disambiguation
+are remembered as well. Moreover, \MATITA{} does it best to ensure that terms
+which require interactive choice are saved in batch compilable format. Thus,
+after evaluating the above theorem the script will be changed to the following
+snippet (assuming that the interpretation of \OP{<} over integers has been
+choosed):
-\texttt{getter}
+\begin{grafite}
+alias symbol "lt" = "integer 'less than'".
+theorem Zlt_compat:
+ \forall x, y, z. x < y \to y < z \to x < z.
+\end{grafite}
+
+But how are disambiguation aliases used? Since they come from the parts of the
+library explicitely included we may be tempted of using them as the only
+available interpretations. This would speed up the disambiguation, but may fail.
+Consider for example:
+
+\begin{grafite}
+theorem lt_mono: \forall x, y, k. x < y \to x < y + k.
+\end{grafite}
-\texttt{cic}
+and suppose that the \OP{+} operator is defined only on natural numbers. If
+the alias for \OP{<} points to the integer version of the operator, no
+refinable partially specified term matching the term could be found.
+
+For this reason we choosed to attempt \emph{multiple disambiguation passes}. A
+first pass attempt to disambiguate using the last available disambiguation
+aliases (\emph{mono aliases} pass), in case of failure the next pass try again
+the disambiguation forgetting the aliases and using the whole library to
+retrieve interpretation for ambiguous expressions (\emph{library aliases} pass).
+Since the latter pass may lead to too many choices we intertwined an additional
+pass among the two which use as interpretations all the aliases coming for
+included parts of the library (\emph{multi aliases} phase). This is the reason
+why aliases are \emph{one-to-many} mappings instead of one-to-one. This choice
+turned out to be a well-balanced trade-off among performances (earlier passes
+fail quickly) and degree of ambiguity supported for presentation level terms.
+
+\subsubsection{Operator instances}
+
+Let's suppose now we want to define a theorem relating ordering relations on
+natural and integer numbers. The way we would like to write such a theorem (as
+we can read it in the \MATITA{} standard library) is:
+
+\begin{grafite}
+include "Z/z.ma".
+include "nat/orders.ma".
+..
+theorem lt_to_Zlt_pos_pos:
+ \forall n, m: nat. n < m \to pos n < pos m.
+\end{grafite}
+
+Unfortunately, none of the passes described above is able to disambiguate its
+type, no matter how aliases are defined. This is because the \OP{<} operator
+occurs twice in the content level term (it has two \emph{instances}) and two
+different interpretations for it have to be used in order to obtain a refinable
+partially specified term. To address this issue, we have the ability to consider
+each instance of a single symbol as a different ambiguous expression in the
+content level term, and thus we can assign a different interpretation to each of
+them. A disambiguation pass which exploit this feature is said to be using
+\emph{fresh instances}.
+
+Fresh instances lead to a non negligible performance loss (since the choice of
+an interpretation for one instances does not constraint the choice for the
+others). For this reason we always attempt a fresh instances pass only after
+attempting a non-fresh one.
+
+\subsubsection{Implicit coercions}
+
+Let's now consider a (rather hypothetical) theorem about derivation:
+
+\begin{grafite}
+theorem power_deriv:
+ \forall n: nat, x: R. d x ^ n dx = n * x ^ (n - 1).
+\end{grafite}
+
+and suppose there exists a \texttt{R \TEXMACRO{to} nat \TEXMACRO{to} R}
+interpretation for \OP{\^}, and a real number interpretation for \OP{*}.
+Mathematichians would write the term that way since it is well known that the
+natural number \texttt{n} could be ``injected'' in \IR{} and considered a real
+number for the purpose of real multiplication. The refiner of \MATITA{} supports
+\emph{implicit coercions} for this reason: given as input the above content
+level term, it will return a partially specified term where in place of
+\texttt{n} the application of a coercion from \texttt{nat} to \texttt{R} appears
+(assuming it has been defined as such of course).
+
+Nonetheless coercions are not always desirable. For example, in disambiguating
+\texttt{\TEXMACRO{forall} x: nat. n < n + 1} we don't want the term which uses
+two coercions from \texttt{nat} to \texttt{R} around \OP{<} arguments to show up
+among the possible partially specified term choices. For this reason in
+\MATITA{} we always try first a disambiguation pass which require the refiner
+not to use the coercions and only in case of failure we attempt a
+coercion-enabled pass.
+
+It is interesting to observe also the relationship among operator instances and
+implicit coercions. Consider again the theorem \texttt{lt\_to\_Zlt\_pos\_pos},
+which \MATITA{} disambiguated using fresh instances. In case there exists a
+coercion from natural numbers to (positive) integers (which indeed does, it is
+the \texttt{pos} constructor itself), the theorem can be disambiguated using
+twice that coercion on the left hand side of the implication. The obtained
+partially specified term however would not probably be the expected one, being a
+theorem which prove a trivial implication. For this reason we choose to always
+prefer fresh instances over implicit coercions, i.e. we always attempt
+disambiguation passes with fresh instances and no implicit coercions before
+attempting passes with implicit coercions.
+
+\subsubsection{Disambiguation passes}
+
+Summarizing, we perform multiple disambiguation passes for each presentation
+level term and in each of them we have 3 degree of freedom: disambiguation
+aliases (mono/multi/library), operator instances (shared/fresh), and implicit
+coercions (enabled/disabled). This would lead to up to 12 different
+disambiguation passes with ordering to be decided upon. Our choice in \MATITA{}
+is depicted in Tab.~\ref{tab:disambpasses}.
+
+\TODO{spiegazione della tabella}
+
+\begin{table}
+ \caption{Disambiguation passes.\strut}
+ \label{tab:disambpasses}
+ \footnotesize
+ \begin{center}
+ \begin{tabular}{c|c|c|c}
+ \multicolumn{1}{p{1.5cm}|}{\centering\raisebox{-1.5ex}{\textbf{Pass}}}
+ & \multicolumn{1}{p{3.1cm}|}{\centering\textbf{Disambiguation aliases}}
+ & \multicolumn{1}{p{2.5cm}|}{\centering\textbf{Operator instances}}
+ & \multicolumn{1}{p{2.5cm}}{\centering\textbf{Implicit coercions}} \\
+ \hline
+ \PASS & Mono aliases & Shared & Disabled \\
+ \PASS & Multi aliases & Shared & Disabled \\
+ \PASS & Mono aliases & Fresh instances & Disabled \\
+ \PASS & Multi aliases & Fresh instances & Disabled \\
+ \PASS & Mono aliases & Fresh instances & Enabled \\
+ \PASS & Multi aliases & Fresh instances & Enabled \\
+ \PASS & Library aliases& Fresh instances & Enabled
+ \end{tabular}
+ \end{center}
+\end{table}
+
+\TODO{alias one shot}
+
+
+
+
+
+
+
+\subsection{Patterns}
-\section{Partially specified terms}
---- il mondo delle tattiche e dintorni ---
serve una intro che almeno cita il widget (per i patterns) e che fa
il resoconto delle cose che abbiamo e che non descriviamo,
sottolineando che abbiamo qualcosa da dire sui pattern e sui
tattichini.\\
-
-
-\subsection{Patterns}
Patterns are the textual counterpart of the MathML widget graphical
selection.
-Matita benefits of a graphical interface and a powerful MathML rendering
+\MATITA{} benefits of a graphical interface and a powerful MathML rendering
widget that allows the user to select pieces of the sequent he is working
on. While this is an extremely intuitive way for the user to
restrict the application of tactics, for example, to some subterms of the
in un pattern phase1only come faccio nell'ultimo esempio. lo si fa
con una pattern\_of(select(pattern))}
-\subsubsection{Comparison with Coq}
-Coq has a two diffrent ways of restricting the application of tactis to
+\subsubsection{Comparison with \COQ{}}
+\COQ{} has a two diffrent ways of restricting the application of tactis to
subterms of the sequent, both relaying on the same special syntax to identify
a term occurrence.
adopting a method for restricting tactics application domain that discourages
using heavy math notation, would definitively be a bad choice.
+
\subsection{Tacticals}
There are mainly two kinds of languages used by proof assistants to recorder
proofs: tactic based and declarative. We will not investigate the philosophy
\item[Proof structuring]
is much easier. Consider for example a proof by induction, and imagine you
are using classical tacticals in one of the state of the
- art graphical interfaces for proof assistant like Proof General or Coq Ide.
+ art graphical interfaces for proof assistant like Proof General or \COQIDE.
After applying the induction principle you have to choose: structure
the proof or not. If you decide for the former you have to branch with
``\texttt{[}'' and write tactics for all the cases separated by
goal) gives you the feeling of what is going on.
\end{description}
+\section{The \MATITA{} library}
+
+\MATITA{} is \COQ{} compatible, in the sense that every theorem of \COQ{}
+can be read, checked and referenced in further developments.
+However, in order to test the actual usability of the system, a
+new library of results has been started from scratch. In this case,
+of course, we wrote (and offer) the source script files,
+while, in the case of \COQ, \MATITA{} may only rely on XML files of
+\COQ{} objects.
+The current library just comprises about one thousand theorems in
+elementary aspects of arithmetics up to the multiplicative property for
+Eulers' totient function $\phi$.
+The library is organized in five main directories: $logic$ (connectives,
+quantifiers, equality, $\dots$), $datatypes$ (basic datatypes and type
+constructors), $nat$ (natural numbers), $Z$ (integers), $Q$ (rationals).
+The most complex development is $nat$, organized in 25 scripts, listed
+in Figure\ref{scripts}
+\begin{figure}[htb]
+$\begin{array}{lll}
+nat.ma & plus.ma & times.ma \\
+minus.ma & exp.ma & compare.ma \\
+orders.ma & le\_arith.ma & lt\_arith.ma \\
+factorial.ma & sigma\_and\_pi.ma & minimization.ma \\
+div\_and\_mod.ma & gcd.ma & congruence.ma \\
+primes.ma & nth\_prime.ma & ord.ma\\
+count.ma & relevant\_equations.ma & permutation.ma \\
+factorization.ma & chinese\_reminder.ma & fermat\_little\_th.ma \\
+totient.ma& & \\
+\end{array}$
+\caption{\label{scripts}\MATITA{} scripts on natural numbers}
+\end{figure}
+
+We do not plan to maintain the library in a centralized way,
+as most of the systems do. On the contary we are currently
+developing wiki-technologies to support a collaborative
+development of the library, encouraging people to expand,
+modify and elaborate previous contributions.
+
+\section{Conclusions}
\acknowledgements
We would like to thank all the students that during the past
five years collaborated in the \HELM{} project and contributed to
-the development of Matita, and in particular
-A.Griggio, F.Guidi, P. Di Lena, L.Padovani, I.Schena, M.Selmi,
-V.Tamburrelli.
+the development of \MATITA{}, and in particular
+M.~Galat\`a, A.~Griggio, F.~Guidi, P.~Di~Lena, L.~Padovani, I.~Schena, M.~Selmi,
+and V.~Tamburrelli.
\theendnotes
\bibliography{matita}
-
\end{document}
projects / helm.git / blobdiff