GAP package XMod (Crossed Modules and Cat1-Groups):
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The GAP 4 package 'XMod'


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.



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


  • 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" );


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


If you have a question relating to 'XMod', encounter any problems, or have a suggestion for extending the package in any way, please