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%W  preface.tex                XMOD documentation               Chris Wensley
%W                                                                & Murat Alp
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%H  $Id: preface.tex,v 2.001 2002/04/19 gap Exp $
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%Y  Copyright (C) 1999,2001 University of St. Andrews, North Haugh,
%Y                          St. Andrews, Fife KY16 9SS, Scotland
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\Chapter{Preface}

\atindex{XMod package}{@XMod package}
The {\XMod} package provides functions for the computation with

\beginlist%unordered
\item{--} crossed modules and cat1-groups;
\item{--} pre-crossed modules, pre-cat1-groups, and their Peiffer quotients;
\item{--} morphisms of these structures;
\item{--} their derivations and sections; and
\item{--} the actor crossed square of a crossed module.
\endlist

It is loaded with the command
\beginexample 
gap> RequirePackage( "xmod" ); 
\endexample

{\XMod} was originally implemented in 1997 using the {\GAP}~3 language.
The first two parts have been converted to {\GAP}~4.
The parts covering derivations; sections and actors will follow in due course.
Many of the function names have been changed during the conversion,
for example `ConjugationXMod' has become `XModByNormalSubgroup'.

\>`InfoXMod' V

In order that the user has some control of the verbosity of the {\XMod}
package's functions, an <InfoClass>  `InfoXMod' is provided
(see Chapter~"ref:Info Functions" in the {\GAP} Reference  Manual for
a description of the `Info' mechanism). By default, the `InfoLevel' of 
`InfoXMod' is `0'; progressively more information is supplied by raising
the `InfoLevel' to levels of `1', `2' and `3', e.g.

\beginexample
gap> SetInfoLevel( InfoXMod, 1); #sets the InfoXMod level to 1
\endexample

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\Section{Authors}

{\XMod} has been developed by

\beginitems
Murat Alp &
Dumlupinar Universitesi,
Fen-Edebiyat Fakultesi, Matematik Bolumu, \hfill\break
Merkez Kampus, Kutahya, Turkey. \hfill\break
e-mail: \Mailto{malp@mail.dumlupinar.edu.tr}

Chris Wensley &
School of Informatics,
University of Wales Bangor, \hfill\break
Dean Street, Bangor, Gwynedd, LL57 1UT, U.K. \hfill\break 
e-mail: \Mailto{c.d.wensley@bangor.ac.uk}
\enditems

Please send bug reports, suggestions and other comments to the second 
of these e-mail addresses.

Additional information can be found on the
*Computational Discrete Algebra* web site at

\hfuzz=20pt%
\URL{http://www.informatics.bangor.ac.uk/public/math/research/hdda/}

\hfuzz=0.1pt%
Copyright {\copyright} 2002 
by Murat Alp and Chris Wensley.

{\XMod} is subject to the {\GAP} copyright regulations as 
detailed in the copyright notice in the {\GAP} manual.

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