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<h1 >idrel</h1 >
<h2>Identities among relations</h2>
<p>
2.49</p>
<p>
2 October 2025
</p>
</div >
<p><b>
Anne Heyworth
</b>
</p><p><b>
Chris Wensley
</b>
<br />Email: <span class="URL" ><a href="mailto:cdwensley.maths@btinternet.com" >cdwensley.maths@btinternet.com</a></span >
<br />Homepage: <span class="URL" ><a href="https://github.com/cdwensley " >https://github.com/cdwensley</a></span >
</p>
<p><a id="X7AA6C5737B711C89" name="X7AA6C5737B711C89" ></a></p>
<h3>Abstract</h3>
<p><strong class="pkg" >IdRel</strong > is a <strong class="pkg" >GAP</strong > package originally implemented in 1999, using the <strong class="pkg" >GAP</strong > 3 language, when the first author was studying for a Ph.D. in Bangor.</p>
<p>This package is designed to compute a minimal set of generators for the module of the identities among relators of a group presentation. It does this using</p>
<ul >
<li ><p>rewriting and logged rewriting: a self-contained implementation of the Knuth-Bendix process using the monoid presentation associated to the group presentation;</p>
</li >
<li ><p>monoid polynomials: an implementation of the monoid ring;</p>
</li >
<li ><p>module polynomials: an implementation of the right module over this monoid generated by the relators.</p>
</li >
<li ><p>Y-sequences: used as a <em >rewriting</em > way of representing elements of a free crossed module (products of conjugates of group relators and inverse relators).</p>
</li >
</ul >
<p><strong class="pkg" >IdRel</strong > became an accepted <strong class="pkg" >GAP</strong > package in May 2015.</p>
<p>Bug reports, suggestions and comments are, of course, welcome. Please contact the last author at <span class="URL" ><a href="mailto:cdwensley.maths@btinternet.com" >cdwensley.maths@btinternet.com</a></span > or submit an issue at the GitHub repository <span class="URL" ><a href="https://github.com/gap-packages/idrel/issues/ " >https://github.com/gap-packages/idrel/issues/</a></span >.</p>
<p><a id="X81488B807F2A1CF1" name="X81488B807F2A1CF1" ></a></p>
<h3>Copyright</h3>
<p>© 1999-2025 Anne Heyworth and Chris Wensley</p>
<p>The <strong class="pkg" >IdRel</strong > package 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.</p>
<p><a id="X82A988D47DFAFCFA" name="X82A988D47DFAFCFA" ></a></p>
<h3>Acknowledgements</h3>
<p>This documentation was prepared using the <strong class="pkg" >GAPDoc</strong > <a href="chapBib.html#biBGAPDoc" >[LN17]</a> and <strong class="pkg" >AutoDoc</strong > <a href="chapBib.html#biBAutoDoc" >[GH17]</a> packages.</p>
<p>The procedure used to produce new releases uses the package <strong class="pkg" >GitHubPagesForGAP</strong > <a href="chapBib.html#biBGitHubPagesForGAP" >[Hor14]</a> and the package <strong class="pkg" >ReleaseTools</strong >.</p>
<p><a id="X8537FEB07AF2BEC8" name="X8537FEB07AF2BEC8" ></a></p>
<div class="contents" >
<h3>Contents<a id="contents" name="contents" ></a></h3>
<div class="ContChap" ><a href="chap1.html#X7DFB63A97E67C0A1" >1 <span class="Heading" >Introduction</span ></a>
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap1.html#X80F39D77788BD099" >1.1 <span class="Heading" >An illustrative example</span ></a>
</span >
</div >
</div >
<div class="ContChap" ><a href="chap2.html#X7CA8FCFD81AA1890" >2 <span class="Heading" >Rewriting Systems</span ></a>
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap2.html#X7875619E84157FC1" >2.1 <span class="Heading" >Monoid Presentations of FpGroups</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X868422B878B0C380" >2.1-1 FreeRelatorGroup</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X7CBE13927DFF4446" >2.1-2 MonoidPresentationFpGroup</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X78301362834E55AB" >2.1-3 PrintLnUsingLabels</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X7EBBA6A284CC7918" >2.1-4 InitialRulesOfPresentation</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap2.html#X7A1F10597D8FC9A9" >2.2 <span class="Heading" >Rewriting systems for FpGroups</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X858ECE3E807C7363" >2.2-1 RewritingSystemFpGroup</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X83BD6C0A80D88C2C" >2.2-2 OnePassReduceWord</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X7F0CD1EB7C220D40" >2.2-3 OnePassKB</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X844BF013780A746D" >2.2-4 RewriteReduce</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X8412C40B7B2DC8E0" >2.2-5 KnuthBendix</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap2.html#X83CBF2BE8478A728" >2.3 <span class="Heading" >Enumerating elements</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap2.html#X7EDA50068207339D" >2.3-1 ElementsOfMonoidPresentation</a></span >
</div ></div >
</div >
<div class="ContChap" ><a href="chap3.html#X7B8D727485966AF8" >3 <span class="Heading" >Logged Rewriting Systems</span ></a>
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap3.html#X797732E87F1FE197" >3.1 <span class="Heading" >Logged Knuth-Bendix Completion</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap3.html#X7F47FE67829B962A" >3.1-1 InitialLoggedRulesOfPresentation</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap3.html#X80075D5180A8F1A5" >3.1-2 LoggedOnePassKB</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap3.html#X7E550C0078AEDC45" >3.1-3 LoggedRewriteReduce</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap3.html#X87D1E3A578AAAFCB" >3.1-4 LoggedKnuthBendix</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap3.html#X8652CEEF7802DA46" >3.1-5 LoggedRewritingSystemFpGroup</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap3.html#X831A93087918AA5D" >3.2 <span class="Heading" >Logged reduction of a word</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap3.html#X7C5094AF784A8BA7" >3.2-1 LoggedReduceWordKB</a></span >
</div ></div >
</div >
<div class="ContChap" ><a href="chap4.html#X83B25026816C87CE" >4 <span class="Heading" >Monoid Polynomials</span ></a>
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap4.html#X7E8CE44085FE959D" >4.1 <span class="Heading" >Construction of monoid polynomials</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap4.html#X7DE231F282DB8660" >4.1-1 MonoidPolyFromCoeffsWords</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap4.html#X84B1F4CC79983A94" >4.2 <span class="Heading" >Components of a polynomial</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap4.html#X810C636178EA42D0" >4.2-1 Terms</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap4.html#X85C78946877C1FF5" >4.2-2 Monic</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap4.html#X82E04F1086DAAA43" >4.2-3 AddTermMonoidPoly</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap4.html#X832341AB7A04BA45" >4.3 <span class="Heading" >Monoid Polynomial Operations</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap4.html#X86C2C49080691991" >4.3-1 Length</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap4.html#X7A80EA5C7AEA68B1" >4.4 <span class="Heading" >Reduction of a Monoid Polynomial</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap4.html#X7979DE308676398D" >4.4-1 ReduceMonoidPoly</a></span >
</div ></div >
</div >
<div class="ContChap" ><a href="chap5.html#X7B5CEEDF82747121" >5 <span class="Heading" >Module Polynomials</span ></a>
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5.html#X86625AB980F24AA5" >5.1 <span class="Heading" >Construction of module polynomials</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5.html#X7A03D1D881B9976E" >5.1-1 ModulePoly</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5.html#X7BA4DEB7865F82E5" >5.1-2 PrintLnModulePoly</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5.html#X83ECC2D5781DE850" >5.2 <span class="Heading" >Components of a module polynomial</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5.html#X79E2DD9879D9182C" >5.2-1 Terms</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap5.html#X7E57DFF4791C4CAA" >5.3 <span class="Heading" >Module Polynomial Operations</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap5.html#X811C7964873E4062" >5.3-1 AddTermModulePoly</a></span >
</div ></div >
</div >
<div class="ContChap" ><a href="chap6.html#X78038BF07E998E21" >6 <span class="Heading" >Identities Among Relators</span ></a>
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap6.html#X788AFE547F49A8AF" >6.1 <span class="Heading" >Constructing identities</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X7BEE0DBB78F9355E" >6.1-1 RootIdentities</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X7933DDE27D5254A4" >6.1-2 IdentityRelatorSequences</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X7D9664267BC57E09" >6.1-3 LogSequenceLessThan</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X84E1E018809BE464" >6.1-4 ExpandLogSequence</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap6.html#X79EE179E7AD81F44" >6.2 <span class="Heading" >Identities for <span class="SimpleMath" >S_3</span ></span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X8064D8CE783CB70A" >6.2-1 ReduceLogSequences</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X82CCDCDF7BE58F35" >6.2-2 ConjugateByWordLogSequence</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X8220EF3585706C00" >6.2-3 ChangeStartLogSequence</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X7E3DACB581C67E3C" >6.2-4 InverseLogSequence</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X8325D1257B791ABC" >6.2-5 CancelImmediateInversesLogSequence</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap6.html#X82CE16C9788F883A" >6.3 <span class="Heading" >Reducing identities</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X80F769D9796954FC" >6.3-1 LogSequenceRewriteRules</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X82F66A16877FCDFE" >6.3-2 OnePassReduceLogSequence</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X85814EFA81FE864F" >6.3-3 MoveRightLogSequence</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X7EE8CE5E79598779" >6.3-4 SubstituteLogSubsequence</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap6.html#X7D428F9B8054F5FB" >6.4 <span class="Heading" >The original approach</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X7FD998C87BF9AAC9" >6.4-1 IdentitiesAmongRelators</a></span >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X78A94CB77B98ACAA" >6.4-2 IdentityYSequences</a></span >
</div ></div >
<div class="ContSect" ><span class="tocline" ><span class="nocss" > </span ><a href="chap6.html#X8448909D82CF6FE9" >6.5 <span class="Heading" >Partial lists of elements</span ></a>
</span >
<div class="ContSSBlock" >
<span class="ContSS" ><br /><span class="nocss" > </span ><a href="chap6.html#X7FCEF03E7A57C331" >6.5-1 PartialElementsOfMonoidRepresentation</a></span >
</div ></div >
</div >
<div class="ContChap" ><a href="chapBib.html" ><span class="Heading" >References</span ></a></div >
<div class="ContChap" ><a href="chapInd.html" ><span class="Heading" >Index</span ></a></div >
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