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%W  preface.tex                XMOD documentation               Chris Wensley
%W                                                                & Murat Alp
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%H  $Id: preface.tex,v 2.006 2004/09/06 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}

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

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

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

{\XMod} was originally implemented in 1997 using the {\GAP}~3 language.
In April 2002 the first and third parts were converted to {\GAP}~4, 
the pre-structures were added, and version 2.001 was released. 
The final two parts, covering derivations, sections and actors, 
were included in the January 2004 release 2.002 for {\GAP}~4.4.

The current version is 2.006, released on September 6th 2004.

Many of the function names have been changed during the conversion,
for example `ConjugationXMod' has become `XModByNormalSubgroup'.
For a list of name changes see the file `names.pdf' in the `doc' directory.

\>`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 `1', `2' and `3', e.g.

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

The following test file (from the ``xmod'' directory) 
runs all the manual commands.

\beginexample
gap> ReadTest("tst/xmod_manual.tst");
+ Testing constructions of crossed modules and cat1-groups
+ GAP4stones: 0
true
\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@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 Higher-dimensional Discrete Algebra* web site at

\hfuzz=20pt%
\URL{http://www.maths.bangor.ac.uk/chda/}

\hfuzz=0.1pt%
Copyright {\copyright} 2004 
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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