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# The GAP 4 package 'XMod'

## Introduction

This package allows for computation with crossed modules; cat1-groups; morphisms of these structures; derivations of crossed modules and the corresponding sections of cat1-groups.

In October 2015 a new section on isoclinism of crossed modules was added.

Experimental functions for crossed squares and cat2-groups are now included.

## Distribution

 * The 'XMod' package is distributed with the accepted GAP packages, see:
     <https://www.gap-system.org/Packages/xmod.html>
 * It may also be obtained from the GitHub repository at:
     <https://gap-packages.github.io/xmod/>

## Copyright

The 'XMod' package is Copyright {\copyright} Chris Wensley et al, 1997--2017.

'XMod' is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

For details, see <http://www.gnu.org/licenses/gpl.html>

## Installation

 * Unpack `xmod-<version_number>.tar.gz` in the `pkg` subdirectory of the GAP root directory.
 * From within GAP load the package with:

    gap> LoadPackage( "xmod" );

    true

 * The file manual.pdf is in the `doc' subdirectory.

## Contact

If you have a question relating to 'XMod', encounter any problems, or have a suggestion for extending the package in any way, please
 * email: `c.d.wensley@bangor.ac.uk`
 * or report an issue at: <https://github.com/gap-packages/xmod/issues/new>