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<div class="section" lang="en">
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<div class="titlepage"><div><div><h5 class="title">
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<a name="fusion.algorithms.iteration.functions.fold"></a><a href="fold.html" title="fold">fold</a></h5></div></div></div>
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<a name="fusion.algorithms.iteration.functions.fold.description"></a><h6>
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<a name="id1114351"></a>
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<a href="fold.html#fusion.algorithms.iteration.functions.fold.description">Description</a>
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</h6>
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<p>
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Repeatedly applies binary <a href="../../../functional/concepts/poly.html" title=" Polymorphic Function
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Object">Polymorphic
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Function Object</a> <code class="computeroutput"><span class="identifier">f</span></code>
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to each element of a sequence and the previous state.
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</p>
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<a name="fusion.algorithms.iteration.functions.fold.synopsis"></a><h6>
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<a name="id1114398"></a>
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<a href="fold.html#fusion.algorithms.iteration.functions.fold.synopsis">Synopsis</a>
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</h6>
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<pre class="programlisting">
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<span class="keyword">template</span><span class="special"><</span>
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<span class="keyword">typename</span> <span class="identifier">Sequence</span><span class="special">,</span>
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<span class="keyword">typename</span> <span class="identifier">State</span><span class="special">,</span>
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<span class="keyword">typename</span> <span class="identifier">F</span>
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<span class="special">></span>
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<span class="keyword">typename</span> <a href="../metafunctions/fold.html" title="fold"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">fold</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">,</span> <span class="identifier">State</span><span class="special">,</span> <span class="identifier">F</span><span class="special">>::</span><span class="identifier">type</span> <span class="identifier">fold</span><span class="special">(</span>
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<span class="identifier">Sequence</span><span class="special">&</span> <span class="identifier">seq</span><span class="special">,</span> <span class="identifier">State</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">initial_state</span><span class="special">,</span> <span class="identifier">F</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span><span class="special">);</span>
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</pre>
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<div class="table">
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<a name="id1114626"></a><p class="title"><b>Table 1.33. Parameters</b></p>
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<table class="table" summary="Parameters">
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<colgroup>
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<col>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Parameter
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</p>
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</th>
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<th>
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<p>
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Requirement
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</p>
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</th>
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<th>
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<p>
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Description
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">seq</span></code>
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</p>
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</td>
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<td>
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<p>
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A model of <a href="../../../sequences/concepts/forward_sequence.html" title="Forward
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Sequence">Forward
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Sequence</a>,<code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">e</span><span class="special">)</span></code> must be a valid expression for
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each element <code class="computeroutput"><span class="identifier">e</span></code>
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in <code class="computeroutput"><span class="identifier">seq</span></code>
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</p>
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</td>
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<td>
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<p>
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Operation's argument
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">initial_state</span></code>
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</p>
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</td>
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<td>
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<p>
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Any type
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</p>
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</td>
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<td>
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<p>
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Initial state
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<code class="computeroutput"><span class="identifier">f</span></code>
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</p>
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</td>
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<td>
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<p>
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A model of binary <a href="../../../functional/concepts/poly.html" title=" Polymorphic Function
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Object">Polymorphic
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Function Object</a>
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</p>
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</td>
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<td>
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<p>
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Operation's argument
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</p>
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</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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<a name="fusion.algorithms.iteration.functions.fold.expression_semantics"></a><h6>
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<a name="id1114833"></a>
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<a href="fold.html#fusion.algorithms.iteration.functions.fold.expression_semantics">Expression
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Semantics</a>
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</h6>
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<pre class="programlisting">
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<span class="identifier">fold</span><span class="special">(</span><span class="identifier">seq</span><span class="special">,</span> <span class="identifier">initial_state</span><span class="special">,</span> <span class="identifier">f</span><span class="special">);</span>
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</pre>
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<p>
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<span class="bold"><strong>Return type</strong></span>: Any type
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</p>
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<p>
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<span class="bold"><strong>Semantics</strong></span>: Equivalent to <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">eN</span> <span class="special">....</span><span class="identifier">f</span><span class="special">(</span><span class="identifier">e2</span><span class="special">,</span><span class="identifier">f</span><span class="special">(</span><span class="identifier">e1</span><span class="special">,</span><span class="identifier">initial_state</span><span class="special">)))</span></code>
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where <code class="computeroutput"><span class="identifier">e1</span> <span class="special">...</span><span class="identifier">eN</span></code> are the elements of <code class="computeroutput"><span class="identifier">seq</span></code>.
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</p>
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<a name="fusion.algorithms.iteration.functions.fold.complexity"></a><h6>
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<a name="id1115018"></a>
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<a href="fold.html#fusion.algorithms.iteration.functions.fold.complexity">Complexity</a>
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</h6>
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<p>
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Linear, exactly <code class="computeroutput"><a href="../../../sequences/intrinsics/metafunctions/size.html" title="size"><code class="computeroutput"><span class="identifier">result_of</span><span class="special">::</span><span class="identifier">size</span></code></a><span class="special"><</span><span class="identifier">Sequence</span><span class="special">>::</span><span class="identifier">value</span></code> applications of <code class="computeroutput"><span class="identifier">f</span></code>.
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</p>
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<a name="fusion.algorithms.iteration.functions.fold.header"></a><h6>
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<a name="id1115102"></a>
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<a href="fold.html#fusion.algorithms.iteration.functions.fold.header">Header</a>
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</h6>
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<pre class="programlisting">
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<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">algorithm</span><span class="special">/</span><span class="identifier">iteration</span><span class="special">/</span><span class="identifier">fold</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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</pre>
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<a name="fusion.algorithms.iteration.functions.fold.example"></a><h6>
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<a name="id1115197"></a>
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<a href="fold.html#fusion.algorithms.iteration.functions.fold.example">Example</a>
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</h6>
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<pre class="programlisting">
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<span class="keyword">struct</span> <span class="identifier">make_string</span>
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<span class="special">{</span>
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<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">State</span><span class="special">></span>
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<span class="keyword">struct</span> <span class="identifier">result</span>
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<span class="special">{</span>
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<span class="keyword">typedef</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">type</span><span class="special">;</span>
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<span class="special">};</span>
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<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
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<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="keyword">operator</span><span class="special">()(</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">t</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">str</span><span class="special">)</span> <span class="keyword">const</span>
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<span class="special">{</span>
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<span class="keyword">return</span> <span class="identifier">str</span> <span class="special">+</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">lexical_cast</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>(</span><span class="identifier">t</span><span class="special">);</span>
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<span class="special">}</span>
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<span class="special">};</span>
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<span class="special">...</span>
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<span class="keyword">const</span> <a href="../../../sequences/containers/vector.html" title="vector"><code class="computeroutput"><span class="identifier">vector</span></code></a><span class="special"><</span><span class="keyword">int</span><span class="special">,</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">vec</span><span class="special">(</span><span class="number">1</span><span class="special">,</span><span class="number">2</span><span class="special">);</span>
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<span class="identifier">assert</span><span class="special">(</span><a href="fold.html" title="fold"><code class="computeroutput"><span class="identifier">fold</span></code></a><span class="special">(</span><span class="identifier">vec</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">(</span><span class="string">""</span><span class="special">),</span> <span class="identifier">make_string</span><span class="special">())</span> <span class="special">==</span> <span class="string">"12"</span><span class="special">);</span>
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</pre>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><small>Copyright © 2001-2007 Joel de Guzman, Dan Marsden, Tobias
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Schwinger</small></td>
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</tr></table>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="../functions.html"><img src="../../../../images/prev.png" alt="Prev"></a><a accesskey="u" href="../functions.html"><img src="../../../../images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../images/home.png" alt="Home"></a><a accesskey="n" href="accumulate.html"><img src="../../../../images/next.png" alt="Next"></a>
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