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158 lines
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<title>The MPL Reference Manual: Associative Sequence</title>
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<body class="docframe refmanual">
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<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Prev</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Back</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
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<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./sequences.html" class="navigation-link">Sequences</a> / <a href="./concepts.html" class="navigation-link">Concepts</a> / <a href="./associative-sequence.html" class="navigation-link">Associative Sequence</a></td>
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</tr></table><div class="header-separator"></div>
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<div class="section" id="associative-sequence">
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<h1><a class="toc-backref" href="./concepts.html#id1401">Associative Sequence</a></h1>
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<div class="section" id="id29">
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<h3><a class="subsection-title" href="#description" name="description">Description</a></h3>
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<p>An <a class="reference internal" href="./associative-sequence.html">Associative Sequence</a> is a <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a> that allows efficient retrieval of
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elements based on keys. Unlike associative containers in the C++ Standard Library,
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MPL associative sequences have no associated ordering relation. Instead,
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<em>type identity</em> is used to impose an equivalence relation on keys, and the
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order in which sequence elements are traversed during iteration is left
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unspecified.</p>
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</div>
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<div class="section" id="id30">
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<h3><a class="subsection-title" href="#definitions" name="definitions">Definitions</a></h3>
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<ul class="simple" id="value-part">
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<li><span id="key-part"></span>A <em>key</em> is a part of the element type used to identify and retrieve
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the element within the sequence.</li>
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<li>A <em>value</em> is a part of the element type retrievied from the sequence
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by its key.</li>
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</ul>
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</div>
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<div class="section" id="id31">
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<h3><a class="subsection-title" href="#expression-requirements" name="expression-requirements">Expression requirements</a></h3>
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<p>In the following table and subsequent specifications, <tt class="literal"><span class="pre">s</span></tt> is an <a class="reference internal" href="./associative-sequence.html">Associative Sequence</a>,
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<tt class="literal"><span class="pre">x</span></tt> is a sequence element, and <tt class="literal"><span class="pre">k</span></tt> and <tt class="literal"><span class="pre">def</span></tt> are arbitrary types.</p>
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<p>In addition to the requirements defined in <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>,
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the following must be met:</p>
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<table border="1" class="docutils table">
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<colgroup>
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<col width="33%" />
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<col width="38%" />
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<col width="29%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head">Expression</th>
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<th class="head">Type</th>
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<th class="head">Complexity</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td><tt class="literal"><span class="pre"><a href="./has-key.html" class="identifier">has_key</a><s,k>::type</span></tt></td>
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<td>Boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a></td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./count.html" class="identifier">count</a><s,k>::type</span></tt></td>
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<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a></td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./order.html" class="identifier">order</a><s,k>::type</span></tt></td>
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<td><a class="reference internal" href="./integral-constant.html">Integral Constant</a> or <tt class="literal"><span class="pre"><a href="./void.html" class="identifier">void_</a></span></tt></td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a><s,k>::type</span></tt></td>
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<td>Any type</td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./at.html" class="identifier">at</a><s,k,def>::type</span></tt></td>
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<td>Any type</td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><s,x>::type</span></tt></td>
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<td>Any type</td>
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<td>Amortized constant time</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./value-type.html" class="identifier">value_type</a><s,x>::type</span></tt></td>
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<td>Any type</td>
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<td>Amortized constant time</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="section" id="id32">
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<h3><a class="subsection-title" href="#expression-semantics" name="expression-semantics">Expression semantics</a></h3>
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<p>The semantics of an expression are defined only
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where they differ from, or are not defined in <a class="reference internal" href="./forward-sequence.html">Forward Sequence</a>.</p>
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<table border="1" class="docutils table">
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<colgroup>
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<col width="33%" />
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<col width="67%" />
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</colgroup>
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<thead valign="bottom">
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<tr><th class="head">Expression</th>
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<th class="head">Semantics</th>
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</tr>
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</thead>
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<tbody valign="top">
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<tr><td><tt class="literal"><span class="pre"><a href="./has-key.html" class="identifier">has_key</a><s,k>::type</span></tt></td>
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<td>A boolean <a class="reference internal" href="./integral-constant.html">Integral Constant</a> <tt class="literal"><span class="pre">c</span></tt> such that
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<tt class="literal"><span class="pre">c::value</span> <span class="pre">==</span> <span class="pre">true</span></tt> if and only if there is one or more
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elements with the key <tt class="literal"><span class="pre">k</span></tt> in <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./has-key.html">has_key</a>.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./count.html" class="identifier">count</a><s,k>::type</span></tt></td>
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<td>The number of elements with the key <tt class="literal"><span class="pre">k</span></tt> in <tt class="literal"><span class="pre">s</span></tt>;
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see <a class="reference internal" href="./count.html">count</a>.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./order.html" class="identifier">order</a><s,k>::type</span></tt></td>
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<td>A unique unsigned <a class="reference internal" href="./integral-constant.html">Integral Constant</a> associated
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with the key <tt class="literal"><span class="pre">k</span></tt> in the sequence <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./order.html">order</a>.</td>
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</tr>
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<tr><td><pre class="first last literal-block">
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<a href="./at.html" class="identifier">at</a><s,k>::type
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<a href="./at.html" class="identifier">at</a><s,k,def>::type
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</pre>
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</td>
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<td>The first element associated with the key <tt class="literal"><span class="pre">k</span></tt>
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in the sequence <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./at.html">at</a>.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./key-type.html" class="identifier">key_type</a><s,x>::type</span></tt></td>
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<td>The key part of the element <tt class="literal"><span class="pre">x</span></tt> that would be
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used to identify <tt class="literal"><span class="pre">x</span></tt> in <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./key-type.html">key_type</a>.</td>
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</tr>
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<tr><td><tt class="literal"><span class="pre"><a href="./value-type.html" class="identifier">value_type</a><s,x>::type</span></tt></td>
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<td>The value part of the element <tt class="literal"><span class="pre">x</span></tt> that would be
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used for <tt class="literal"><span class="pre">x</span></tt> in <tt class="literal"><span class="pre">s</span></tt>; see <a class="reference internal" href="./value-type.html">value_type</a>.</td>
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</tr>
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</tbody>
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</table>
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<!-- Invariants
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- - - - - - - - - -
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For any associative sequence ``s`` the following invariants always hold:
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* ??? -->
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</div>
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<div class="section" id="id33">
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<h3><a class="subsection-title" href="#models" name="models">Models</a></h3>
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<ul class="simple">
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<li><a class="reference internal" href="./set.html">set</a></li>
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<li><a class="reference internal" href="./map.html">map</a></li>
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</ul>
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<!-- * |multiset| -->
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</div>
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<div class="section" id="id34">
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<h3><a class="subsection-title" href="#see-also" name="see-also">See also</a></h3>
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<p><a class="reference internal" href="./sequences.html">Sequences</a>, <a class="reference internal" href="./extensible-associative-sequence.html">Extensible Associative Sequence</a>, <a class="reference internal" href="./has-key.html">has_key</a>, <a class="reference internal" href="./count.html">count</a>, <a class="reference internal" href="./order.html">order</a>, <a class="reference internal" href="./at.html">at</a>, <a class="reference internal" href="./key-type.html">key_type</a>, <a class="reference internal" href="./value-type.html">value_type</a></p>
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<!-- Sequences/Concepts//Extensible Associative Sequence |80 -->
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</div>
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</div>
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<div class="footer-separator"></div>
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<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Prev</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./back-extensible-sequence.html" class="navigation-link">Back</a> <a href="./extensible-associative-sequence.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./concepts.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
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<td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body>
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