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<TITLE> Christian Urban </TITLE>
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<B>Links</B><BR>
<A HREF="http://www4.in.tum.de/~urbanc/index.html">Home</A><BR>
<A HREF="http://www4.in.tum.de/~urbanc/Cut/cutapplet.html">Applet Home</A><BR><BR><p>
<B>Java Versions</B><BR>
<A HREF="http://www4.in.tum.de/~urbanc/Cut/CL.html">CL</A><BR>
<A HREF="http://www4.in.tum.de/~urbanc/Cut/LJT.html">LJT</A><BR>
<A HREF="http://www4.in.tum.de/~urbanc/Cut/ND.html">ND</A><BR><BR>
<B>Plugin Versions</B><BR>
<A HREF="http://www4.in.tum.de/~urbanc/Cut/CL-plugin.html">CL</A><BR>
<A HREF="http://www4.in.tum.de/~urbanc/Cut/LJT-plugin.html">LJT</A><BR>
<A HREF="http://www4.in.tum.de/~urbanc/Cut/ND-plugin.html">ND</A><BR>
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<A HREF="http://isabelle.in.tum.de/nominal/">
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<H2>Cut-Elimination in Herbelin's calculus for intuitionistic logic</H2>
Recommended reading for this applet is a paper by Dyckhoff and Urban,
[<A HREF="http://www-theory.dcs.st-and.ac.uk/~rd/publications/MJES/DyckhoffUrbanWestApp01.rev.ps">ps</A>,
<A HREF="http://www-theory.dcs.st-and.ac.uk/~rd/publications/MJES/DyckhoffUrbanWestApp01.rev.pdf">pdf</A>].
Mayor difference between the standard sequent calculus and Herbelin's sequent calculus
is that in the cut-free fragment "there are no semantically
trivial permutations of the inference rules, where by 'semantically trivial' we mean
'interpreted in NJ as true equations between to (normal) deductions'"
(from [<A HREF="http://www-theory.dcs.st-and.ac.uk/~rd/publications/SLPaper.corr.ps">ps</A>]).
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<B>How to use it?</B>
If your browser is working correctly, then you will see a window
with two examples (more added if you suggest some). When pressing on
one of the buttons, a new window will pop up. What follows
is a brief explanation of all the features available in this window.
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<B>Buttons and Keys</B>
<UL>
<LI> The buttons
<IMG SRC="http://www4.in.tum.de/~urbanc/Cut/x.jpg">
`fire' cuts (not all cuts necessarily have such buttons).
<LI> If you use the <B>left mouse button</B> for pressing on those buttons,
then the new proof will appear inside the window. Whereas if you use
the <B>right mouse button</B>, a new window will pop up and
the new proof will be displayed in this window. Use the right mouse
button if you want to compare a proof and its reduct.
<LI> The keys <B>Page-up</B> and <B>Page-down</B> zoom in or out of a proof
respectively.
</UL>
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<B>Menu Functions</B>
<UL>
<LI> <B>Zoom in</B> and <B>Zoom out</B> work like Page-up and Page-down,
respectively.
<LI> <B>Unicode</B> If this radiobutton is switched on, logic symbols
are displayed in unicode, otherwise in ascii. (This is for the
poor guys who have a browser and/or operating system which cannot handle
unicode.)
<LI> <B>Labels</B> As mentioned earlier the sequents are composed of
two sets of labelled
formulae, not multisets of formulae as in the standard formulation
of sequent calculus. Enabling this radiobutton causes that labels are
drawn. Use this when you are unsure where implicit contractions are.
<LI> <B>Compact printing</B> In the paper referred above weakening
is done only in axioms. If this radiobutton is switched on (default),
then, in order to save space, formulae are weakened as soon as possible.
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Last modified: Sat Mar 3 05:17:09 CET 2007
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