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<title>GLEP 61 -- Manifest2 compression</title>
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<table class="rfc2822 docutils field-list" frame="void" rules="none">
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<col class="field-name" />
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<col class="field-body" />
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<tbody valign="top">
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<tr class="field"><th class="field-name">GLEP:</th><td class="field-body">61</td>
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</tr>
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<tr class="field"><th class="field-name">Title:</th><td class="field-body">Manifest2 compression</td>
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</tr>
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<tr class="field"><th class="field-name">Version:</th><td class="field-body">1.7</td>
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</tr>
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<tr class="field"><th class="field-name">Last-Modified:</th><td class="field-body"><a class="reference external" href="http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/proj/en/glep/glep-0061.txt?cvsroot=gentoo">2010/04/07 21:34:24</a></td>
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</tr>
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<tr class="field"><th class="field-name">Author:</th><td class="field-body">Robin Hugh Johnson <robbat2 at gentoo.org></td>
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</tr>
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<tr class="field"><th class="field-name">Status:</th><td class="field-body">Draft</td>
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</tr>
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<tr class="field"><th class="field-name">Type:</th><td class="field-body">Standards Track</td>
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</tr>
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<tr class="field"><th class="field-name">Content-Type:</th><td class="field-body"><a class="reference external" href="glep-0002.html">text/x-rst</a></td>
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</tr>
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<tr class="field"><th class="field-name">Requires:</th><td class="field-body"><a class="reference external" href="http://www.gentoo.org/proj/en/glepglep-0044.html">44</a></td>
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</tr>
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<tr class="field"><th class="field-name">Created:</th><td class="field-body">July 2008</td>
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</tr>
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<tr class="field"><th class="field-name">Updated:</th><td class="field-body">October 2008, January 2010</td>
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</tr>
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<tr class="field"><th class="field-name">Updates:</th><td class="field-body">44</td>
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</tr>
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<tr class="field"><th class="field-name">Post-History:</th><td class="field-body">December 2009, January 2010</td>
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</tr>
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</tbody>
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</table>
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<hr />
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<div class="contents topic" id="contents">
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<p class="topic-title first">Contents</p>
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<ul class="simple">
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<li><a class="reference internal" href="#abstract" id="id1">Abstract</a></li>
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<li><a class="reference internal" href="#motivation" id="id2">Motivation</a></li>
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<li><a class="reference internal" href="#specification" id="id3">Specification</a><ul>
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<li><a class="reference internal" href="#creation-of-compressed-manifests" id="id4">Creation of compressed Manifests:</a></li>
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<li><a class="reference internal" href="#validation-of-manifests" id="id5">Validation of Manifests:</a></li>
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</ul>
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</li>
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<li><a class="reference internal" href="#example-results-with-a-32kib-cut-off-gzip-algorithm" id="id6">Example Results with a 32KiB cut-off, gzip algorithm</a></li>
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<li><a class="reference internal" href="#backwards-compatibility" id="id7">Backwards Compatibility</a></li>
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<li><a class="reference internal" href="#references" id="id8">References</a></li>
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<li><a class="reference internal" href="#copyright" id="id9">Copyright</a></li>
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</ul>
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</div>
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<div class="section" id="abstract">
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<h1><a class="toc-backref" href="#id1">Abstract</a></h1>
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<p>Deals with compression of large Manifest2 files.</p>
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</div>
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<div class="section" id="motivation">
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<h1><a class="toc-backref" href="#id2">Motivation</a></h1>
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<p>With the introduction of MetaManifest, and full-tree Manifest coverage,
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we are faced with the possibility of having very large Manifests.</p>
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<p>Preliminary experiments with MetaManifest, show that with just the
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existing per-package Manifests, the full MetaManifest (top-level only,
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no first-level sub directories), for a tree including metadata/, exceeds
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8MiB in size. Applying common compression can achieve a 50-60% reduction
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in this size.</p>
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<p>Additionally, some of the larger already-existing Manifests in the tree
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can also be reduced.</p>
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<p>This GLEP is not mandatory for the tree-signing specification, but
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instead helps to cut down the size impact of large Manifest2 files, some
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of which are already present in the tree. As such, it is also able to
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stand on it's own.</p>
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</div>
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<div class="section" id="specification">
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<h1><a class="toc-backref" href="#id3">Specification</a></h1>
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<div class="section" id="creation-of-compressed-manifests">
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<h2><a class="toc-backref" href="#id4">Creation of compressed Manifests:</a></h2>
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<p>32KiB is suggested as a arbitrary cut-off point to start generating
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compressed Manifest2 files.</p>
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<p>The compression must only applied during the creation of a tree intended
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for end users. No Manifests stored in a VCS should be compressed in the
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VCS. For the main gentoo-portage tree, this means that the compressed
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Manifests should be generated using the CVS to Rsync process.</p>
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<p>The Manifest compression process is required to ensure that inconsistent
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compressed versions do not exist.</p>
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</div>
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<div class="section" id="validation-of-manifests">
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<h2><a class="toc-backref" href="#id5">Validation of Manifests:</a></h2>
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<p>When searching for a Manifest2 file, if the basename form does not
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exist, the package manager should search in the same location using
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common compressed suffixes, and use the compressed file in place of the
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Manifest2.</p>
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<p>gzip, bzip2, lzma, xz should all be supported if available on the given
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platform. In the case that multiple versions exist, the package manager
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should simply pick one - they should be identical, differing only in
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compression.</p>
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</div>
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</div>
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<div class="section" id="example-results-with-a-32kib-cut-off-gzip-algorithm">
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<h1><a class="toc-backref" href="#id6">Example Results with a 32KiB cut-off, gzip algorithm</a></h1>
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<p>As of 2010/01/30, the suggested cut-off would impact the following 21 existing
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Manifests, for a saving of nearly 900KiB:</p>
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<pre class="literal-block">
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Size Path
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65788 app-doc/linux-gazette/Manifest
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75739 app-office/openoffice-bin/Manifest
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40534 app-text/texlive-core/Manifest
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41710 dev-texlive/texlive-bibtexextra/Manifest
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38197 dev-texlive/texlive-documentation-english/Manifest
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129610 dev-texlive/texlive-fontsextra/Manifest
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36022 dev-texlive/texlive-humanities/Manifest
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686118 dev-texlive/texlive-latexextra/Manifest
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43392 dev-texlive/texlive-latexrecommended/Manifest
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33375 dev-texlive/texlive-mathextra/Manifest
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39781 dev-texlive/texlive-pictures/Manifest
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69567 dev-texlive/texlive-pstricks/Manifest
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75460 dev-texlive/texlive-publishers/Manifest
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50879 dev-texlive/texlive-science/Manifest
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36711 kde-base/kde-l10n/Manifest
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36539 media-gfx/bootsplash-themes/Manifest
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33058 net-fs/autofs/Manifest
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39781 www-client/firefox-bin/Manifest
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48983 www-client/icecat/Manifest
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60213 www-client/mozilla-firefox/Manifest
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39065 x11-themes/gkrellm-themes/Manifest
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</pre>
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<p>Additionally, with the MetaManifest proposal, the following new manifests would
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also be compressed, for a saving of nearly 4MiB:</p>
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<pre class="literal-block">
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Size Path
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33442 app-admin/Manifest
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71073 app-dicts/Manifest
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35923 app-emacs/Manifest
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45808 app-misc/Manifest
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50169 app-text/Manifest
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112786 dev-java/Manifest
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65581 dev-libs/Manifest
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42619 dev-lisp/Manifest
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182163 dev-perl/Manifest
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96198 dev-python/Manifest
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58963 dev-ruby/Manifest
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59736 dev-util/Manifest
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58338 eclass/Manifest
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55749 kde-base/Manifest
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110064 licenses/Manifest
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35262 media-gfx/Manifest
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53995 media-libs/Manifest
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55607 media-plugins/Manifest
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71911 media-sound/Manifest
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34835 media-video/Manifest
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5747849 metadata/Manifest
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47452 net-analyzer/Manifest
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65989 net-misc/Manifest
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316787 profiles/Manifest
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67784 sys-apps/Manifest
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48971 x11-misc/Manifest
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41475 x11-plugins/Manifest
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</pre>
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</div>
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<div class="section" id="backwards-compatibility">
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<h1><a class="toc-backref" href="#id7">Backwards Compatibility</a></h1>
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<p>The package Manifests should also be maintained as ONLY uncompressed in
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CVS.</p>
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<p>For processing of all existing per-package Manifests, if compression is
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used, it should be done in parallel to the existing Manifests, to
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provide for a changeover period. Newer versions of Portage may later
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choose to exclude all non-compressed Manifests during emerge --sync if
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compressed versions are guaranteed to exist on the servers.</p>
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<p>MetaManifests may come into existence as compressed from the start, as
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do not have an backwards compatibility issues.</p>
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<p>As a side note, this breaks all manual interaction with Manifests
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such as grep, and so should only be applied to large Manifest2 files,
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such as the MetaManifest.</p>
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</div>
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<div class="section" id="references">
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<h1><a class="toc-backref" href="#id8">References</a></h1>
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<table class="docutils citation" frame="void" id="glep44" rules="none">
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<colgroup><col class="label" /><col /></colgroup>
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<tbody valign="top">
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<tr><td class="label">[GLEP44]</td><td>Mauch, M. (2005) GLEP44 - Manifest2 format.
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<a class="reference external" href="http://www.gentoo.org/proj/en/glep/glep-0044.html">http://www.gentoo.org/proj/en/glep/glep-0044.html</a></td></tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="copyright">
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<h1><a class="toc-backref" href="#id9">Copyright</a></h1>
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<p>Copyright (c) 2008-2010 by Robin Hugh Johnson. This material may be
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distributed only subject to the terms and conditions set forth in the
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Open Publication License, v1.0.</p>
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