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Douglas Gregor
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ref.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<html>
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<html>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta http-equiv="refresh" content="0; URL=../../doc/html/ref.html">
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<title>Boost: ref.hpp documentation</title>
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<body>
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<body bgcolor="White">
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Automatic redirection failed, please go to
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<table border="0" width="100%">
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<a href="../../doc/html/ref.html">../../doc/html/ref.html</a>
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<tr>
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<td width="277">
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<img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" width="277" height="86">
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<td align="center">
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<table border="0">
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<tr>
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<td nowrap><h1>ref.hpp</h1>
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</td>
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</tr>
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<tr>
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<td align="right" nowrap><small> 1.00.0004 (2002-01-27)</small></td>
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</tr>
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</table>
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</td>
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</tr>
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<tr>
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<td colspan="2" height="64"> </td>
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</tr>
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</table>
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<h2>Files</h2>
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<ul>
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<li>
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<a href="../../boost/ref.hpp">ref.hpp</a>
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</ul>
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<h2>Purpose</h2>
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<p>
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The header <a href="../../boost/ref.hpp">boost/ref.hpp</a> defines the class
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template <b>boost::reference_wrapper<T></b>, the two functions <b>boost::ref</b>
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and <b>boost::cref</b> that return instances of <b>boost::reference_wrapper<T></b>,
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and the two traits classes <b>boost::is_reference_wrapper<T></b> and <b>boost::unwrap_reference<T></b>.
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</p>
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<p>
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The purpose of <b>boost::reference_wrapper<T></b> is to contain a
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reference to an object of type <b>T</b>. It is primarily used to "feed"
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references to function templates (algorithms) that take their parameter by
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value.
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</p>
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<p>
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To support this usage, <b>boost::reference_wrapper<T></b> provides an
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implicit conversion to <b>T &</b>. This usually allows the function
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templates to work on references unmodified.
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</p>
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<p>
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<b>boost::reference_wrapper<T></b> is both <b>CopyConstructible</b> and <b>Assignable</b>
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(ordinary references are not <b>Assignable</b>).
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</p>
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<p>
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The expression <b>boost::ref(x)</b> returns a <b>boost::reference_wrapper<X>(x)</b>
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where <b>X</b> is the type of <b>x</b>. Similarly, <b>boost::cref(x)</b> returns
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a <b>boost::reference_wrapper<X const>(x)</b>.
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</p>
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<p>
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The expression <b>boost::is_reference_wrapper<T>::value</b> is <b>true</b>
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if <b>T</b> is a <b>reference_wrapper</b>, and <b>false</b>
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otherwise.
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</p>
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<p>
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The type-expression <b>boost::unwrap_reference<T>::type</b> is <b>T::type</b>
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if <b>T</b> is a <b>reference_wrapper</b>, <b>T</b> otherwise.
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</p>
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<h2>Interface</h2>
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<h3>Synopsis</h3>
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<pre>
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namespace boost
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{
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template<class T> class <a href="#reference_wrapper">reference_wrapper</a>;
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template<class T> reference_wrapper<T> <a href="#ref">ref</a>(T & t);
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template<class T> reference_wrapper<T const> <a href="#cref">cref</a>(T const & t);
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template<class T> class is_reference_wrapper<T const>;
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template<class T> class unwrap_reference<T const>;
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}
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</pre>
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<h3><a name="reference_wrapper">reference_wrapper</a></h3>
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<pre>
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template<class T> class reference_wrapper
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{
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public:
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typedef T type;
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explicit <a href="#rt_construct">reference_wrapper</a>(T & t);
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<a href="#rt_operator">operator T &</a> () const;
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T & <a href="#rt_get">get</a>() const;
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T* <a href="#rt_get_pointer">get_pointer</a>() const;
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};
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</pre>
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<h4><a name="rt_construct">explicit reference_wrapper(T & t)</a></h4>
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<blockquote>
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<p>
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<b>Effects:</b> Constructs a <b>reference_wrapper</b> object that stores a
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reference to <b>t</b>.
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</p>
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<p>
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<b>Throws:</b> Nothing.
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</p>
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</blockquote>
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<h4><a name="rt_operator">operator T & () const</a></h4>
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<blockquote>
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<p>
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<b>Returns:</b> the stored reference.
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</p>
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<p>
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<b>Throws:</b> Nothing.
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</p>
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</blockquote>
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<h4><a name="rt_get">T & get() const</a></h4>
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<blockquote>
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<p>
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<b>Returns:</b> the stored reference.
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</p>
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<p>
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<b>Throws:</b> Nothing.
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</p>
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</blockquote>
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<h4><a name="rt_get_pointer">T* get_pointer() const</a></h4>
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<blockquote>
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<p>
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<b>Returns:</b> a pointer to the stored object.
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</p>
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<p>
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<b>Throws:</b> Nothing.
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</p>
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</blockquote>
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<h3><a name="ref">ref</a></h3>
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<pre>
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template<class T> reference_wrapper<T> ref(T & t);
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</pre>
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<blockquote>
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<p>
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<b>Returns:</b> <tt>reference_wrapper<T>(t)</tt>.
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</p>
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<p>
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<b>Throws:</b> Nothing.
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</p>
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</blockquote>
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<h3><a name="cref">cref</a></h3>
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<pre>
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template<class T> reference_wrapper<T const> cref(T const & t);
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</pre>
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<blockquote>
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<p>
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<b>Returns:</b> <tt>reference_wrapper<T const>(t)</tt>.
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</p>
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<p>
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<b>Throws:</b> Nothing.
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</p>
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</blockquote>
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<h3><a name="is_reference_wrapper">is_reference_wrapper</a></h3>
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<pre>
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template<class T> class is_reference_wrapper<T const>
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{
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public:
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static bool value = <i>unspecified</i>;
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};
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</pre>
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Value is <b>true</b> iff <tt>T</tt> is a specialization of <tt>reference_wrapper</tt>.
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<h3><a name="unwrap_reference">unwrap_reference</a></h3>
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<pre>
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template<class T> class unwrap_reference<T const>
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{
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public:
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typedef <i>unspecified</i> type;
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};
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</pre>
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<tt>type</tt> is equivalent to <tt>T::type</tt> if <tt>T</tt> is a
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specialization of <tt>reference_wrapper</tt>. Otherwise <tt>type</tt> is
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equivalent to <tt>T</tt>.
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<h2>Acknowledgements</h2>
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<p>
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<b>ref</b> and <b>cref</b> were originally part of the Boost.Tuple library by <a href="../../people/jaakko_jarvi.htm">
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Jaakko Järvi</a>. They were "promoted to <b>boost::</b> status" by <a href="../../people/peter_dimov.htm">
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Peter Dimov</a> because they are generally useful. <a href="../../people/doug_gregor.html">
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Douglas Gregor</a> and <a href="../../people/dave_abrahams.htm">Dave Abrahams</a>
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contributed <tt>is_reference_wrapper</tt> and <tt>unwrap_reference</tt>.
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</p>
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<p><br>
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<br>
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<br>
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<small>Copyright © 2001 by Peter Dimov and Multi Media Ltd. Permission to
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copy, use, modify, sell and distribute this document is granted provided this
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copyright notice appears in all copies. This document is provided "as
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is" without express or implied warranty, and with no claim as to its
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suitability for any purpose.</small></p>
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</body>
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</html>
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