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<div class="ChapSects"><a href="chap9.html#X810C43BC7F63C4B4">9 <span class="Heading">Development history</span></a>
<div class="ContSect"><span class="nocss"> </span><a href="chap9.html#X7ACE7E8384B73156">9.1 <span class="Heading">Changes from version to version</span></a>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap9.html#X848198AA862249C4">9.1-1 <span class="Heading">Version 1 for <strong class="pkg">GAP</strong> 3</span></a>
</span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap9.html#X7CF8E72D80AAB54F">9.1-2 <span class="Heading">Version 2</span></a>
</span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap9.html#X7F9CE0487BB6F660">9.1-3 <span class="Heading">Version 2.001 for <strong class="pkg">GAP</strong> 4</span></a>
</span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap9.html#X7966FF497C36C465">9.1-4 <span class="Heading">Induced crossed modules</span></a>
</span>
<span class="ContSS"><br /><span class="nocss"> </span><a href="chap9.html#X7E0B70FD82DC5BA8">9.1-5 <span class="Heading">Versions 2.002 -- 2.006</span></a>
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<span class="ContSS"><br /><span class="nocss"> </span><a href="chap9.html#X7F6E650E85384C25">9.1-6 <span class="Heading">Versions 2.007 -- 2.010</span></a>
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<span class="ContSS"><br /><span class="nocss"> </span><a href="chap9.html#X7A71BD747D1AA4A5">9.1-7 <span class="Heading">Version 2.12</span></a>
</span>
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<div class="ContSect"><span class="nocss"> </span><a href="chap9.html#X83D1530487593182">9.2 <span class="Heading">What needs doing next?</span></a>
</div>
</div>
<h3>9 <span class="Heading">Development history</span></h3>
<p>This chapter, which contains details of the major changes to the package as it develops, was first created in April 2002. Details of the changes from <strong class="pkg">XMod</strong> 1 to <strong class="pkg">XMod</strong> 2.001 are far from complete. Starting with version 2.009 the file <code class="file">CHANGES</code> lists the minor changes as well as the more fundamental ones.</p>
<p>The inspiration for this package was the need, in the mid-1990's, to calculate induced crossed modules (see <a href="chapBib.html#biBBW1">[BW95]</a>, <a href="chapBib.html#biBBW2">[BW96]</a>, <a href="chapBib.html#biBBW3">[BW03]</a>). <strong class="pkg">GAP</strong> was chosen over other computational group theory systems because the code was freely available, and it was possible to modify the Tietze transformation code so as to record the images of the original generators of a presentation as words in the simplified presentation. (These modifications are now a standard part of the Tietze transformation package in <strong class="pkg">GAP</strong>.)</p>
<p><a id="X7ACE7E8384B73156" name="X7ACE7E8384B73156"></a></p>
<h4>9.1 <span class="Heading">Changes from version to version</span></h4>
<p><a id="X848198AA862249C4" name="X848198AA862249C4"></a></p>
<h5>9.1-1 <span class="Heading">Version 1 for <strong class="pkg">GAP</strong> 3</span></h5>
<p>The first version of <strong class="pkg">XMod</strong> became an accepted package for <strong class="pkg">GAP</strong> 3.4.3 in December 1996.</p>
<p><a id="X7CF8E72D80AAB54F" name="X7CF8E72D80AAB54F"></a></p>
<h5>9.1-2 <span class="Heading">Version 2</span></h5>
<p>Conversion of <strong class="pkg">XMod</strong> 1 from <strong class="pkg">GAP</strong> 3.4.3 to the new <strong class="pkg">GAP</strong> syntax began soon after <strong class="pkg">GAP</strong> 4 was released, and had a lengthy gestation. The new <strong class="pkg">GAP</strong> syntax encouraged a re-naming of many of the function names. An early decision was to introduce generic names <code class="code">2dObject</code> for (pre-)crossed modules and (pre-)cat1-groups, and <code class="code">2dMapping</code> for the various types of morphism. In 2.009 <code class="code">3dObject</code> is used for crossed squares and cat2-groups, and <code class="code">3dMapping</code> for their morphisms. A generic name for derivations and sections is also required, and <code class="code">Up2dMapping</code> is currently used.</p>
<p><a id="X7F9CE0487BB6F660" name="X7F9CE0487BB6F660"></a></p>
<h5>9.1-3 <span class="Heading">Version 2.001 for <strong class="pkg">GAP</strong> 4</span></h5>
<p>This was the first version of <strong class="pkg">XMod</strong> for <strong class="pkg">GAP</strong> 4, completed in April 2002 in a rush to catch the release of <strong class="pkg">GAP</strong> 4.3. Functions for actors and induced crossed modules were not included, nor many of the functions for derivations and sections, for example <code class="code">InnerDerivation</code>.</p>
<p><a id="X7966FF497C36C465" name="X7966FF497C36C465"></a></p>
<h5>9.1-4 <span class="Heading">Induced crossed modules</span></h5>
<p>During the period May 20th - May 27th 2002 converted <code class="file">induce.g</code> to <code class="file">induce.gd</code> and <code class="file">induce.gi</code> (later renamed <code class="file">induce2.gd</code>, <code class="file">induce2.gi</code>), at least as regards induced crossed modules. (Induced cat1-groups may be convereted one day.) For details, see the file <code class="file">CHANGES</code>.</p>
<p><a id="X7E0B70FD82DC5BA8" name="X7E0B70FD82DC5BA8"></a></p>
<h5>9.1-5 <span class="Heading">Versions 2.002 -- 2.006</span></h5>
<p>Version 2.002 was prepared for the 4.4 release at the end of January 2004.</p>
<p>Version 2.003 of February 28th 2004 just fixed some file protections.</p>
<p>Version 2.004 of April 14th 2004 added the <code class="code">Cat1Select</code> functionality of version 1 to the <code class="code">Cat1</code> function (see also version 2.007).</p>
<p>Version 2.005 of April 16th 2004 moved the example files from <code class="file">tst/test_i.g</code> to <code class="file">examples/example_i.g</code>, and converted <code class="file">testmanual.g</code> to a proper test file <code class="file">tst/xmod_manual.tst</code>.</p>
<p>A significant change was the conversion of the actor crossed module functions from the <code class="file">3.4.4</code> version, including <code class="code">AutomorphismPermGroup</code> for a crossed module, <code class="code">WhiteheadXMod</code>, <code class="code">NorrieXMod</code>, <code class="code">LueXMod</code>, <code class="code">ActorXMod</code>, <code class="code">Centre</code> of a crossed module, <code class="code">InnerMorphism</code> and <code class="code">InnerActorXMod</code>.</p>
<p><a id="X7F6E650E85384C25" name="X7F6E650E85384C25"></a></p>
<h5>9.1-6 <span class="Heading">Versions 2.007 -- 2.010</span></h5>
<p>These versions contain changes made between September 2004 and October 2007.</p>
<ul>
<li><p>Added basic functions for crossed squares, considered as <code class="code">3dObjects</code> with crossed pairings, and their morphisms. Groups with two normal subgroups, and the actor of a crossed module, provide standard examples of crossed squares. (Cat2-groups are not yet implemented.)</p>
</li>
<li><p>Converted the documentation to the format of the <strong class="pkg">GAPDoc</strong> package.</p>
</li>
<li><p>Improved <code class="code">AutomorphismPermGroup</code> for crossed modules, and introduced a special method for conjugation crossed modules.</p>
</li>
<li><p>Substantial revisons made to <code class="code">XModByCentralExtension</code>, <code class="code">NorrieXMod</code>, <code class="code">LueXMod</code>, <code class="code">ActorXMod</code>, and <code class="code">InclusionInducedXModByCopower</code>.</p>
</li>
<li><p>Reintroduced the <code class="code">Cat1Select</code> operation.</p>
</li>
<li><p>Version 2.010, of October 2007, was timed to coincide with the release of <strong class="pkg">GAP</strong> 4.4.10, and included a change of filenames; correct file protection codes; and an improvement to <code class="code">AutomorphismPermGroup</code> for crossed modules.</p>
</li>
</ul>
<p><a id="X7A71BD747D1AA4A5" name="X7A71BD747D1AA4A5"></a></p>
<h5>9.1-7 <span class="Heading">Version 2.12</span></h5>
<p>This latest version was released in November 2008.</p>
<ul>
<li><p>The file <code class="code">CHANGES</code> was introduced, so that minor corrections need no longer be listed in this chapter.</p>
</li>
<li><p>The file <code class="code">makedocrel.g</code> was copied, with appropriate changes, from <strong class="pkg">GAPDoc</strong>, and now provides the correct way to update the documentation.</p>
</li>
<li><p>The first functions for crossed modules of groupoids were introduced.</p>
</li>
<li><p>The package webpage has moved along with the whole of the Bangor Maths website: <span class="URL"><a href="http://www.maths.bangor.ac.uk/">http://www.maths.bangor.ac.uk/</a></span>.</p>
</li>
<li><p>A GNU General Public License declaration has been added.</p>
</li>
</ul>
<p><a id="X83D1530487593182" name="X83D1530487593182"></a></p>
<h4>9.2 <span class="Heading">What needs doing next?</span></h4>
<ul>
<li><p>Speed up the calculation of Whitehead groups.</p>
</li>
<li><p>Add more functions for <code class="code">3dObjects</code> and implement <code class="code">cat2-groups</code>.</p>
</li>
<li><p>Add interaction with package <strong class="pkg">Gpd</strong> implementing group groupoid version of a crossed module and crossed modules over groupoids.</p>
</li>
<li><p>Add interaction with <strong class="pkg">IdRel</strong>, <strong class="pkg">XRes</strong>, and <strong class="pkg">natp</strong>.</p>
</li>
<li><p>Need <code class="code">InverseGeneralMapping</code> for morphisms.</p>
</li>
<li><p>Need more features for <code class="code">FpXMods</code>, <code class="code">PcXMods</code>, etc.</p>
</li>
<li><p>Implement actions of a crossed module.</p>
</li>
<li><p>Implement <code class="code">FreeXMods</code>.</p>
</li>
<li><p>Implement an operation <code class="code">Isomorphism2dObjects</code>.</p>
</li>
<li><p>Allow the construction of a group of morphisms of crossed modules.</p>
</li>
<li><p>Complete the conversion from Version 1 of the calculation of sections using <code class="code">EndoClasses</code>.</p>
</li>
</ul>
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