1 Preface

Sections

Authors

The XMod package provides functions for the computation with

crossed modules and cat1-groups;
pre-crossed modules, pre-cat1-groups, and their Peiffer quotients;
morphisms of these structures;
their derivations and sections; and
the actor crossed square of a crossed module.

It is loaded with the command

gap> RequirePackage( "xmod" );

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 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.

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

1.1 Authors

XMod has been developed by

Murat Alp: Dumlupinar Universitesi, Fen-Edebiyat Fakultesi, Matematik Bolumu,
Merkez Kampus, Kutahya, Turkey.
e-mail: malp@mail.dumlupinar.edu.tr
Chris Wensley: School of Informatics, University of Wales Bangor,
Dean Street, Bangor, Gwynedd, LL57 1UT, U.K.
e-mail: c.d.wensley@bangor.ac.uk

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

http://www.informatics.bangor.ac.uk/public/math/research/hdda/

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

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XMod manual
May 2002