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<HTML lang=en>
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<TITLE> Christian Urban </TITLE>
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<BASE HREF="http://www4.in.tum.de/~urbanc/">
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</HEAD>
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<BODY TEXT="#000000"
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BGCOLOR="#000080"
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LINK="#0000EF"
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VLINK="#51188E"
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ALINK="#FF0000">
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<TABLE WIDTH="100%"
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COLS="2"
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BGCOLOR="#000080"
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BORDER="0"
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FRAME="none"
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CELLPADDING="10"
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CELLSPACING="2"
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RULES="COLS,ROWS">
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<TR>
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<TD BGCOLOR="#FFFFFF"
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WIDTH="24%"
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VALIGN="TOP"
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ROWSPAN="2">
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<B>Links</B><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/index.html">Home</A><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/Cut/cutapplet.html">Applet Home</A><BR><BR>
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<B>Java Versions</B><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/Cut/CL.html">CL</A><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/Cut/LJT.html">LJT</A><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/Cut/ND.html">ND</A><BR><BR>
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<B>Plugin Versions</B><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/Cut/CL-plugin.html">CL</A><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/Cut/LJT-plugin.html">LJT</A><BR>
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<A HREF="http://www4.in.tum.de/~urbanc/Cut/ND-plugin.html">ND</A><BR>
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<BR>
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<BR>
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<A HREF="http://isabelle.in.tum.de/nominal/">
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<IMG SRC="ribbon.gif" ALT="" style="width: 114px; height: 100px;" align="left">
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</A>
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</TD>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<H2>What is the Semantics for Classical Logic?</H2>
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In the intuitionistic case, the answer to this question is well-understood -
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essentially a semantics is given to all proofs in normal form and all other
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proofs inherit this semantics from the normal forms they reduce to. This
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implies that:
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<blockquote>
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(1) reductions preserving the semantics of a proof.
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</blockquote>
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It is widely known that this assumption causes any reasonable semantics
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for classical logic to collaps. In the literature Lafont's example is
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often cited for this observation.<p>
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<center>
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<IMG SRC="Cut/lafont1.jpg" ALT="" ALIGN=CENTER>
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</center><p>
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<center>
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<IMG SRC="Cut/lafont2.jpg" ALT="" ALIGN=CENTER>
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<IMG SRC="Cut/lafont3.jpg" ALT="" ALIGN=CENTER>
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</center><p>
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</TD>
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</TR>
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</TABLE>
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<P><!-- Created: Tue Jul 3 21:01:42 BST 2001 -->
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<!-- hhmts start -->
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Last modified: Sat Mar 3 05:17:53 CET 2007
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<!-- hhmts end -->
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</BODY>
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</HTML>
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