## &XMod;

Crossed modules and cat1-groups in &GAP;
Version 2.010
Murat Alp malp@dumlupinar.edu.tr

          Dumlupinar Universitesi,

          Fen-Edebiyat Fakultesi, Matematik Bolumu

          Merkez Kampus, Kutahya, Turkey.

Chris Wensley c.d.wensley@bangor.ac.uk http://www.informatics.bangor.ac.uk/~cwensley/

          School of Informatics, University of Wales Bangor,

          Dean Street, Bangor, Gwynedd, LL57 1UT, U.K.

October 2007

The XMod package provides functions for computation with finite crossed modules and cat1-groups, and morphisms of these structures; finite pre-crossed modules, pre-cat1-groups, and their Peiffer quotients; derivations of crossed modules and sections of cat1-groups; the actor crossed square of a crossed module; and crossed squares and their morphisms (experimental version).

&copyright; 1997-2007 by Murat Alp and Chris Wensley

We adopt the copyright regulations of &GAP; as detailed in the copyright notice in the &GAP; manual.
&XMod; was originally implemented in 1997 using the &GAP;3 language. when the first author was studying for a Ph.D. in Bangor.

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 2.010, released on October 8th 2007.

Bug reports, suggestions and comments are, of course, welcome. Please contact the second author at c.d.wensley@bangor.ac.uk.
The first author wishes to acknowledge support from Dumlupinar University and the Turkish government.
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