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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<TITLE>Homepage of Christian Urban</TITLE>
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<B>Links</B><BR>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/index.html">Home</A><BR>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/publications.html">Publications</A><BR>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/teaching.html">Teaching</A><BR>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/travelling.html">Recent Talks</A><BR>
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<A HREF="http://isabelle.in.tum.de/nominal/">My Research Group</A>
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<BR>
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<BR>
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<B>Handy Information</B><BR>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/logic.html">People in Logic</A><BR>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/programming.html">Programming Languages</A><BR>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/misc.html">Miscellaneous</A>
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<BR><BR>
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<A HREF="http://isabelle.in.tum.de/nominal/">
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<IMG SRC="nominal-logo.gif" ALT="" style="border-width: 0px;" align="left"></A>
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<A NAME="Home"></A>
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<TABLE>
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<TD WIDTH="75%">
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<H1>Christian Urban</H1>
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<B>E-mail</B>
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urbanc <I>at</I> dcs kcl ac uk<BR>
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<BR>
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<B>Address</B>
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<A HREF="http://www.dcs.kcl.ac.uk">Department of Informatics</A>,
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<A HREF="http://www.kcl.ac.uk">King's College London</A>,
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Strand, London WC2R 2LS, UK. My office is S6.30 on the 6th floor of the Strand Building.
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<BR><BR>
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<B>Fax</B> +44 20 7848 2851
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/picture-small.jpg"><IMG ALT="" SRC="picture-small.jpg" align="top"></A>
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</TABLE>
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<p>
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<IMG SRC="new.gif" ALT="" style="" align="left"><A HREF="http://isabelle.in.tum.de/nominal/activities/idp" target="_top">Isabelle Documentation Project</A> (contains now a draft of a 200-page tutorial on Isabelle programming)<BR>
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</TD>
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</TR>
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<TR>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<B>Current Position</B>
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I am a lecturer in the Department of Informatics at King's College London.
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This is similar to a position of an assistant professor in other places. In 2011,
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I was also offered a lectureship
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<A HREF="http://www.it.uu.se/" TITLE="Uppsala">here</A>, an associate professorship
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<A HREF="http://www.itu.dk/en/" TITLE="ITU, Copenhagen">here</A>,
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and full professorships
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<A HREF="http://www.ustcsz.edu.cn/kedweb/" TITLE="IAS, Suzhou">here</A> and
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<A HREF="http://www.sei.ecnu.edu.cn/apps/portal/home.html" TITLE="Shanghai">here</A>.
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I thank all people involved for their efforts.
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<P>
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<B>Past Positions</B>
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In April 2006, I was awarded an <A HREF="http://en.wikipedia.org/wiki/Emmy_Noether">Emmy-Noether</A>
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<A HREF="http://www.dfg.de/en/research_funding/programmes/individual/emmy_noether/in_brief/index.html">fellowship</A>, which I held at the <A HREF="http://www.in.tum.de/en.html">TU Munich</A> until
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September 2011.
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Between September 2008 and February 2009, I was an invited research fellow in
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the <A HREF="http://www.cs.princeton.edu/">Department of Computer Science</A> in Princeton.
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In 2004/05 I was an Alexander-von-Humboldt fellow in Munich and
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from 2000 until 2004 I was awarded a Research Fellowship in Cambridge. Before that
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I did my PhD in Cambridge.
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<P>
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<B>Research Interests</B> theorem provers, programming languages, compilers,
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algorithms, proof theory, type systems, concurrency, lambda calculus, unification,
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regular expressions, computability, complexity, functional and logic programming.
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<P>
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<B>Conferences</B>
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<A HREF="http://www.iiia.csic.es/~levy/unif06/">UNIF'06</A> (member of PC),
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<A HREF="http://www.cs.mcgill.ca/~bpientka/lfmtp07">LFMTP'07</A> (member of PC),
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<A HREF="http://isabelle.in.tum.de/nominal/activities/lfmtp08/">LFMTP'08</A> (PC co-chair),
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<A HREF="http://www.cis.upenn.edu/~sweirich/wmm/">WMM'08</A> (member of PC),
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<A HREF="http://www.mat.ufmg.br/lsfa2008/">LSFA'08</A> (invited speaker),
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<A HREF="http://www.dcs.kcl.ac.uk/staff/maribel/TAASN.html">TAASN'09</A> (member of PC),
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<A HREF="http://lsfa09.cic.unb.br/">LSFA'09</A> (member of PC),
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<A HREF="http://isabelle.in.tum.de/nominal/activities/tphols09/idw.html">IDW'09</A> (organiser),
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<A HREF="http://www.seas.upenn.edu/~sweirich/wmm/wmm09.html">WMM'09</A> (PC chair),
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<A HREF="http://tphols.in.tum.de/">TPHOLs'09</A> (PC co-chair),
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<A HREF="http://dream.inf.ed.ac.uk/events/automatheo-2010/">Automatheo'10</A> (member of PC),
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<A HREF="http://www.floc-conference.org/">ITP'10</A> (member of PC),
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<A HREF="http://www.dcs.kcl.ac.uk/staff/maribel/UNIF.html">UNIF'10</A> (invited speaker),
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<A HREF="http://www.cis.upenn.edu/~bcpierce/wmm/">WMM'10</A> (invited speaker),
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<A HREF="http://isabelle.in.tum.de/nominal/activities/idw10/idw.html">IDW'10</A> (co-organiser),
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<A HREF="http://formes.asia/cpp">CPP'11</A> (member of PC),
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<A HREF="http://www.rdp2011.uns.ac.rs/rta/">RTA'11</A> (member of PC),
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<A HREF="http://lfmtp11.cs.umn.edu">LFMTP'11</A> (member of PC)
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<BR>
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</TD>
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</TR>
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<TR>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<B>Nominal Isabelle</B>
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I currently work on Nominal
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<A HREF="http://isabelle.in.tum.de">Isabelle</A>. This is joint work with
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<A HREF="http://wwwbroy.in.tum.de/~berghofe/">Dr Stefan Berghofer</A>,
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<A HREF="http://www4.in.tum.de/~wenzelm/">Dr Markus Wenzel</A>,
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<A HREF="http://www4.in.tum.de/~kaliszyk/">Dr Cezary Kaliszyk</A> and
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the Isabelle-team in Munich.
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Many of the theoretical ideas originate from the nominal logic project - a wonderful project headed
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by <A HREF="http://www.cl.cam.ac.uk/~amp12/">Prof. Andrew Pitts</A>.
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The aim of my work is to make formal reasoning involving binders as simple as
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on paper and the hope is to lure
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<A HREF="http://alliance.seas.upenn.edu/~plclub/cgi-bin/poplmark/index.php?title=The_POPLmark_Challenge#Vision">masses</A> to automated
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theorem proving. My funding for this work was provided in 2004 and 2005 by a research
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fellowship from the
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<A HREF="http://en.wikipedia.org/wiki/Alexander_von_Humboldt">Alexander-von-Humboldt</A>
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<A HREF="http://www.humboldt-foundation.de/web/home.html">foundation</A>. During this time I was a visitor in the group of
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<A HREF="http://www.mathematik.uni-muenchen.de/~schwicht/">Prof. Helmut Schwichtenberg</A>.
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Since 2006 this work is supported by an
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<A HREF="http://en.wikipedia.org/wiki/Emmy_Noether">Emmy-Noether</A>
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<A HREF="http://www.dfg.de/en/research_funding/programmes/individual/emmy_noether/in_brief/index.html">fellowship</A>.
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There is a <A HREF="http://isabelle.in.tum.de/nominal/">webpage</A> and a
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<A HREF="https://mailmanbroy.informatik.tu-muenchen.de/mailman/listinfo/nominal-isabelle">mailing list</A>
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about Nominal Isabelle. It also includes a list of projects that use Nominal Isabelle.
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Users of Nominal Isabelle had their papers appearing at LICS, POPL, FOSSACS, SOS, TPHOLs and CPP.
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</TD>
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</TR>
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<TR>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<B>Myhill-Nerode and Regular Expressions</B>
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Out of frustration of having to teach inductions in theorem provers using worn-out examples like
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fib and even/odd, we implemented a large part of regular language theory in Isabelle/HOL.
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This <A HREF="http://afp.sourceforge.net/devel-entries/Myhill-Nerode.shtml">implementation</A>
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gives rise to much more interesting examples, as shown
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<A HREF="http://www.cs.cmu.edu/~rwh/papers/regexp/jfp.ps">here</A> and
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<A HREF="http://ropas.snu.ac.kr/~kwang/paper/06-jfp-yi.pdf">here</A>. It turns out that
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formalisations of automata theory are a huge
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<A HREF="https://lists.cam.ac.uk/pipermail/cl-isabelle-users/2005-September/msg00012.html">pain</A>
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in theorem provers, especially in those that are HOL-based.
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We therefore went against the
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<A HREF="http://books.google.com/books?id=8lKyxS8_CNoC&pg=PA14&source=gbs_toc_r&cad=4#v=onepage&q&f=false">mainstream</A>
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and used in our formalisation regular expressions exclusively,
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because they are much more convenient for formal reasoning. The results we
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formalised include: the Myhill-Nerode theorem, the closure of regular languages
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under complementation, finiteness of derivatives of regular expressions and a surprising
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result about Subseq, which according to
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this
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<A HREF="http://blog.computationalcomplexity.org/2006/01/theorem-that-should-be-better-known.html">blog</A>
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should be better known. This is joint work with Prof. Xingyuan
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Zhang and his student Chunhan Wu from the
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<A HREF="http://www.ust.com.cn/">PLA University of Science and Technology</A> in Nanjing.
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My funding for this work came from the
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<A HREF="http://www.sinogermanscience.org.cn/">Chinese-German Research Centre</A>.
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</TD>
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</TR>
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<TR>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<B>Nominal Unification and Alpha-Prolog</B>
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/Unification">Nominal unification</A> is one outcome of
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my involvement in the nominal logic project in Cambridge. Another is the logic programming language
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alpha-Prolog (joint work with <A HREF="http://homepages.inf.ed.ac.uk/jcheney/">Dr James Cheney</A>),
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which uses nominal unification - click for details
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<A HREF="http://homepages.inf.ed.ac.uk/jcheney/programs/aprolog/">here</A>.
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The nominal unification algorithm has been
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/Unification">formally verified</A> in Isabelle. This
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was possible since this unification algorithm is formulated in a simple first-order language
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(unlike other algorithms for higher-order unification).
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<A HREF="http://www.cs.indiana.edu/~dfried/">Prof. Daniel Friedman</A> and his group use nominal
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unification in their alpha-Kanren system implemented in Scheme.
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<A HREF="http://www.dcs.kcl.ac.uk/staff/maribel/">Prof. Maribel Fernandez</A> and her student
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improved the nominal unification algorithm to be quadratic.
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My funding for this work was provided through a research fellowship from
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<A HREF="http://www.corpus.cam.ac.uk">Corpus Christi College</A>, Cambridge.
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</TD>
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</TR>
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<TR>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<B>Classical Logic</B>
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I was Ph.D. student in the University of Cambridge
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<A HREF="http://www.cl.cam.ac.uk">Computer Laboratory</A>
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and for three years
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called Gonville and Caius College my home. I was very lucky to have
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<A HREF="http://research.microsoft.com/~gmb/">Dr Gavin Bierman</A>
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as supervisor. My research in Cambridge was also very much influenced by
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<A HREF="http://www.dpmms.cam.ac.uk/~martin/">Prof. Martin Hyland</A>.
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Some details on my thesis "Classical Logic and Computation" are
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/PhD/index.html">elsewhere</A>, including
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a <A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/Cut/cutapplet.html">Java Applet</A> that
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'visualises' some of the results from the thesis. I completed the writing of
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the thesis in <A HREF="http://iml.univ-mrs.fr/ldp/">Marseille</A> in the group of
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<A HREF="http://iml.univ-mrs.fr/~girard/">Prof. Jean-Yves Girard</A>. My study in
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Cambridge was funded by two <A HREF="http://www.daad.de/index.html">scholarships</a>
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from the German government; my year in Marseille by a TMR-fellowship from the EU.
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My PhD was also one starting point for the EPSRC Project on the Semantics of Classical
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Proofs. The strong normalisation result in the PhD has recently been used by
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<A HREF="http://www.loria.fr/~ckirchne/hot.html">Prof. Claude Kirchner</A> and his
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students to prove consistency for their superdeduction system lemuridae.
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</TD>
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</TR>
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<TR>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<B>Forum</B>
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I implemented Forum, a programming language based on classical linear logic,
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as my M.Phil. thesis. This was joint work with
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<A HREF="http://www.dcs.st-and.ac.uk/~rd/">Dr Roy Dyckhoff</A>.
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Details can be found
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<A HREF="http://www.dcs.st-and.ac.uk/~rd/logic/nonmac/">here</A> and
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<A HREF="http://www.lix.polytechnique.fr/Labo/Dale.Miller/forum/">here</A>. During my
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M.Phil study I spent one month in Philadelphia invited by
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<A HREF="http://www.lix.polytechnique.fr/~dale/">Prof. Dale Miller</A>.
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</TD>
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</TR>
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<TR>
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<TD BGCOLOR="#FFFFFF" WIDTH="75%">
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<B>G4ip</B> An implementation of G4ip using the imperative language Pizza can be found
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<A HREF="http://www.dcs.kcl.ac.uk/staff/urbanc/Prover/index.html">here</A>.
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<A HREF="http://pizzacompiler.sourceforge.net">Pizza</A> is a conservative
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extension of Java and a precursor of Scala. The implementation illustrates the technique of success
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continuations.
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</TD>
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</TR>
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</TABLE>
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