232 lines
9.3 KiB
HTML
232 lines
9.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<meta http-equiv="content-type" content="text/html; charset=UTF-8">
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<title>RS01, RS02 and RS03</title>
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<link rel="stylesheet" type="text/css" href="../include/dvdisaster.css">
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</head>
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<body>
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<!-- Title header -->
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<table width="100%" cellpadding="0" border="0">
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<tr>
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<td align="left">
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<span class="fxxl"><b>dvdisaster</b></span>
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<i>Version 0.72.4 / 0.72 (pl4)</i>
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</td>
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<td align="right">
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<span class="fxxl"> </span><a href="http://dvdisaster.net/en/">To the Internet version</a>
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<a href="../cs/qa33.html"></a>
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<a href="../de/qa33.html"></a>
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<a href="../ru/qa33.html"></a>
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</td>
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</tr>
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</table>
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<!-- Language chooser or separator -->
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<table width="100%" cellpadding="0" border="0">
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<tr>
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<td colspan="2" class="hsep"></td>
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</tr>
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<tr><td colspan="2" style="height: 10px">
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</td></tr>
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</table>
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<!-- Main body (Navigation, actual page content, optional news column) -->
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<table width="100%" cellspacing=0>
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<tr>
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<!-- Navigation -->
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<td style="background-color:#f0f0f0; vertical-align:top; width:20%;">
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<table width="100%" cellpadding="10">
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<tr>
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<td>
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<span class="fs"><b>Contents</b></span>
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<table width="100%" cellpadding="0" cellspacing="0">
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<tr>
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<td class="hsep"></td>
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</tr>
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</table><p>
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<table width="100%">
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<tr><td colspan=3><span class="fs"><a href="news.html">News</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="index.html">Overview</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="howtos.html">Howtos</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="download.html">Download</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="qa.html">Questions and Answers</a></span></td></tr>
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<tr><td style="width:1%; vertical-align:top;">·</td><td colspan=2><span class="fs"><a href="qa10.html">Technical Questions</a></span></td></tr>
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<tr><td style="width:1%; vertical-align:top;">·</td><td colspan=2><span class="fs"><a href="qa20.html">Error messages</a></span></td></tr>
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<tr><td style="width:1%; vertical-align:top;">·</td><td colspan=2><span class="fs"><a href="qa30.html">Background information</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa31.html">Error correction properties</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa32.html">Image level data recovery</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs">RS01, RS02 and RS03</span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa34.html">Linear reading strategy</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa35.html">Adaptive reading strategy</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa36.html">Remarks on read errors</a></span></td></tr>
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<tr><td></td><td style="vertical-align:top; font-size:small;">-</td><td><span class="fs"><a href="qa37.html">Hints for storing the error correction files</a></span></td></tr>
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<tr><td></td><td></td><td style="height:10px;"></td></tr>
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<tr><td colspan=3><span class="fs"><a href="feedback.html">Bug reporting</a></span></td></tr>
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</table>
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</td>
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</tr>
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</table>
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</td>
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<td></td>
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<!-- Actual page contents -->
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<td style="vertical-align:top; width:77%;" rowspan="2">
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<!-- Insert actual page content below -->
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<h3 class="top">The RS01, RS02 and RS03 methods</h3>
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dvdisaster contains three error correction methods.
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RS01 and RS02 are the existing and proven methods while RS03 is still
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under development.<p>
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<b>Comparison of the methods.</b>
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All three methods build on the same
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<a href="qa31.html">Reed-Solomon</a> error correction.
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They calculate error correction information for ISO images which
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is used to recover unreadable sectors if the disc becomes damaged afterwards.<p>
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The methods differ in the way the error correction information is stored:<p>
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<ul>
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<li>
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<a name="file"> </a>
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RS01 creates <b>error correction files</b> which are stored separately from
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the image they belong to. Since data protection at the
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<a href="qa32.html#file">file level</a> is difficult,
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error correction files must be stored on media which are protected
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against data loss by dvdisaster, too.<p></li>
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<li>
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<a name="image"> </a>
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To apply the RS02 method an image is first created on hard disc using a
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CD/DVD writing software. Before the image is written on the medium,
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dvdisaster is used to <b>augment the image</b> with error correction data.
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Therefore the data to be protected and the error correction information
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are located at the same medium. Damaged sectors in the error correction
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information reduce the data recovery capacity, but do not make recovery
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impossible - a second medium for keeping or protecting the error correction
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information is not required.<p></li>
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</ul>
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RS03 is a further development of RS01 and RS02. It can create both
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error correction files and augmented images:
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<ul>
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<li>RS03 can distribute work over multiple processor cores and is therefore
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much faster than RS01/RS02 on modern hardware.</li>
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<li>RS03 <b>error correction files</b> are - contrary to RS01 - robust against
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damage. This should not delude you into careless handling of your error
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correction files though - the disadvantages of <a href="qa32.html#file">reading
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at the filesystem level</a> are still valid.</li>
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<li>RS03 <b>augmented images</b> do not require so-called master blocks
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holding important information. This makes RS03 a bit more robust, but also
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more restrictive: The augmented image must completely fill the medium now
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while the size of augmented image can be freely chosen in RS02.
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</li>
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</ul>
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The changes for parallel computation and higher robustness make RS03 a bit less
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space efficient, e.g. RS03 error correction data has slighly less error
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correction capacity than its RS01/RS02 counterpart with equal size.<p>
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<a name="table"> </a>
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<b>Comparison of error correction storage.</b><p>
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The following table summarizes the differences between
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error correction files (RS01, RS03) and augmented images (RS02, RS03):<p>
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<table width="100%" border="1" cellspacing="0" cellpadding="5">
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<tr>
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<td class="w50p"><i>Error correction files</i></td>
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<td class="w50p"><i>Image augmented with error correction data</i></td>
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</tr>
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<tr valign="top">
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<td>
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any possible redundancy can be chosen</td>
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<td> redundancy is limited by free space on medium<br>
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(= medium capacity - size of data image)</td>
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</tr>
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<tr valign="top">
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<td>already effective at 15% redundancy
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since error correction files are required to be free of damage</td>
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<td>requires more redundancy (recommended: 20-30%)
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to compensate defects in the error correction data</td>
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</tr>
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<tr valign="top">
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<td>medium can be completely filled with data</td>
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<td>usable medium capacity is reduced by amount of error correction data</td>
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</tr>
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<tr valign="top">
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<td> can be created for already existing media</td>
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<td> only applicable before writing the new medium since
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the image must be augmented with error correction information in advance</td>
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</tr>
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<tr valign="top">
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<td> separately storing the error correction file from user data
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strengthens data protection</td>
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<td> common storage of user data and error correction data may reduce error
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correction capacity</td>
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</tr>
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<tr valign="top">
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<td>Mapping between error correction files and media must be kept.
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Error correction files must be protected against damage.</td>
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<td>Easy one-medium solution; error correction information
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needs not to be cataloged or explicitly protected.</td></tr>
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<tr valign="top">
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<td> no compatibilty issues with play-back units</td>
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<td> media with augmented images may not play correctly on all units</td>
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</tr>
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</table><p>
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<!-- do not change below -->
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</td> <!-- end of page contents -->
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</tr>
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<!--
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</td>
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<td></td>
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<tr><td colspan="2" style="width:100%; height:10px;"></td>
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<tr><td colspan="2" class="hsep"></td>
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</tr>
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<tr>
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<td align="center">
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<span class="fs">
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<i> Copyright 2004-2012 Carsten Gnörlich.<br>
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Verbatim copying and distribution of this entire article is permitted in any medium, provided this notice is preserved.
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</i>
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</span>
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</td>
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</tr>
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<tr><td colspan="2" class="hsep"></td>
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</tr>
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</table>
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</body>
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</html>
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