\chapter*{Introduction}
\label{sec:intro}

The \Vauc software platform is dedicated to the computation with
finite state automata.  Here, `finite state automata' is to be
understood in the broadest sense: \emph{weighted} automata on a free
monoid --- that is, automata that not only accept, or recognize,
\emph{words} but compute for every word a \emph{multiplicity} which is
taken a priori in \emph{an arbitrary semiring} --- and even weighted
automata on \emph{non free monoids}.  The latter become far too
general objects.  As for now, are implemented in \Vauc only the
(weighted) automata on (direct) products of free monoids, machines
that are often called \emph{transducers} --- that is automata that
realize (weighted) relations between words\footnote{When the relation
  is ``weighted'' the multiplicity has to be taken in a
  \emph{commutative} semiring.}.

When designing \Vauc, we had three main goals in mind: we wanted
\begin{enumerate}
\item a \emph{general purpose} software,
\item a software that allows a programming style natural to computer
  scientists who work with automata and transducers,
\item  an open and free software.
\end{enumerate}

This is the reason why we implemented so to say \emph{on top} of the
\Vauc platform a library that allows to apply a number of functions on
automata, and even to define and edit automata, without having to
bother with subtleties of \Cxx programming.  The drawback of this is
obviously that the user is given a \emph{fixed} set of functions that
apply to \emph{already typed} automata.  This library of functions
does not allow to write new algorithms on automata but permits to
combine or compose without much difficulties nor efforts a rather
large set of commands.  We call it \tafkit, standing for \emph{Typed
  Automata Function Kit}, as these commands take as input, and output,
automata whose type is fixed.  \tafkit is presented in
\autoref{sec:tafkit}.


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