| author | Christian Urban <christian.urban@kcl.ac.uk> |
| Tue, 16 May 2023 21:44:03 +0100 | |
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ROWSPAN="9"> |
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<B>Links</B><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/index.html">Home</A><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/publications.html">Publications</A><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/teaching.html">Teaching</A><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/travelling.html">Recent Talks</A><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/Nominal/">Nominal Isabelle</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="https://nms.kcl.ac.uk/christian.urban/logic.html">People in Logic</A><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/programming.html">Programming Languages</A><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/misc.html">Miscellaneous</A> |
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<BR><BR> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/Nominal/"> |
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<IMG SRC="nominal-logo.gif" ALT="" style="border-width: 0px;" align="left"></A> |
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</td> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/Cookbook/"> |
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<IMG SRC="Cookbook/logo-documentation.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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<H1>Christian Urban</H1> |
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<B>E-mail</B> |
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christian.urban <I>at</I> kcl ac uk<BR> |
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<BR> |
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<B>Address</B> |
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<A HREF="http://www.kcl.ac.uk/nms/depts/informatics/">Department of Informatics</A>, |
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<A HREF="http://www.kcl.ac.uk">King's College London</A>, |
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Bush House, 30 Aldwych, London WC2B 4BG, UK. My office is 7.07 on the 7th floor, North Wing, of the Bush House. |
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<BR> |
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</TD> |
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<TD align="right" valign="top"> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/picture-small.jpg"><IMG ALT="" SRC="picture-small.jpg" align="top"></A> |
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<p> |
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<IMG SRC="new.gif" ALT="" style="" align="left"><A HREF="https://nms.kcl.ac.uk/christian.urban/Cookbook" target="_top">Isabelle Programming Tutorial</A> (draft of a 200-page tutorial on Isabelle programming - updated to |
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<A HREF="http://isabelle.in.tum.de">Isabelle 2019</A> thanks to Norbert Schirmer)<BR><BR> |
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</TD> |
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<TD BGCOLOR="#FFFFFF" WIDTH="75%"> |
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<B>Current Position</B> |
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Since 2011 I have been 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://en.itu.dk/" TITLE="ITU, Copenhagen">here</A>, |
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and full professorships |
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<A HREF="https://en.wikipedia.org/wiki/University_of_Science_and_Technology_of_China" TITLE="IAS, Suzhou">here</A> and |
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<A HREF="https://en.wikipedia.org/wiki/East_China_Normal_University" 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="https://www.dfg.de/en/research_funding/programmes/individual/emmy_noether/">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 scientist 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 funded by two scholarships from the German Academic Exchange |
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Service (<A HREF="http://www.daad.de/index.html">DAAD</A>). |
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<P> |
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<B>Skolem Award 2015</B> Together with |
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<A HREF="http://www.pps.univ-paris-diderot.fr/~tasson/">Christine Tasson</A>, I was awarded a |
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<A HREF="http://cadeinc.org/Skolem-Award">Thoralf Skolem Award</A>, a ten-year |
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test-of-time award from CADE. This was for our |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/Publications/nom-cade-05.ps">paper</A> |
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on Nominal Techniques in Isabelle/HOL from 2005. The Skolem Award award was given also |
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to Nicolaas de Bruijn, Zohar Manna and |
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Nachum Derschowitz, amongst others. |
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<P> |
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<B>Research Interests</B> theorem provers, verification, programming languages, compilers, |
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algorithms, security, proof theory, type systems, concurrency, lambda calculus, unification, |
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regular expressions, computability, complexity, functional and logic programming. |
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<B>Teaching</B> I usually enjoy teaching. At King's my students nominated me for the Teaching |
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Excellence Award in |
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2012, 2015, 2016 and 2017, and for the best MSc Project supervisor in 2015. |
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In 2014 I received both prizes for Best UG Project Supervisor and for Best |
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MSc Project Supervisor in the <A HREF="http://www.kcl.ac.uk/nms/index.aspx">NMS Faculty</A>. |
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In 2020/21, I was again nominated for the King's Education Award with a very kind |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/nomination2021.pdf">citation</A> from a student. |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/nomination2022.pdf">Here</A> is the citation from |
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2021/22. Another <A HREF="https://nms.kcl.ac.uk/christian.urban/nomination2023.pdf">one</A> for 2022/23. |
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<P> |
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<B>Conferences</B> |
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UNIF'06 (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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LFMTP'08 (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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LSFA'08 (invited speaker), |
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<A HREF="http://www.inf.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="https://nms.kcl.ac.uk/christian.urban/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="https://nms.kcl.ac.uk/christian.urban/Nominal/activities/tphols09/">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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UNIF'10 (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="https://nms.kcl.ac.uk/christian.urban/Nominal/activities/idw10/idw.html">IDW'10</A> (co-organiser), |
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CPP'11 (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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<A HREF="http://www.cs.uwyo.edu/~ruben/itp-2014">ITP'14</A> (member of PC), |
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<A HREF="http://www.cicm-conference.org/2015/cicm.php?event=mkm">MKM'15</A> (member of PC), |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/itp-2015/">ITP'15</A> (PC co-chair), |
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<A HREF="https://itp2016.inria.fr">ITP'16</A> (member of PC) |
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<A HREF="http://lsfa.cic.unb.br">LSFA'17</A> (member of PC) |
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<A HREF="http://itp2017.cic.unb.br">ITP'17</A> (member of PC) |
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<A HREF="https://itp19.cecs.pdx.edu">ITP'19</A> (member of PC) |
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<A HREF="https://ijcar2020.org">IJCAR'20</A> (member of PC) |
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<A HREF="http://easyconferences.eu/itp2021bid/">ITP'21</A> (member of PC) |
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<A HREF="http://www.cs.cmu.edu/~mheule/CADE28/">CADE'21</A> (member of PC) |
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<P> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/itp-2015/">ITP'15</A> took place in Nanjing organised |
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by Xingyuan Zhang and me<BR> |
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<p> |
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<B>Current PhD</B> Chengsong Tan<BR> |
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<B>Former PhD</B> Fahad Ausaf (works at ARM in the VHDL compiler team)<BR> |
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<B>Former RAs</B> Chunhan Wu, <A HREF="http://cl-informatik.uibk.ac.at/users/cek/">Cezary Kaliszyk</A>, |
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<A HREF="http://dpt-info.u-strasbg.fr/~narboux/">Julien Narboux</A><p> |
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If I am not teaching or not doing any research, I am sometimes in the lavender |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/family.jpg">fields</A> of London, or I do |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/c.jpg">model-shoots</A> far away, or I am |
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assistant to the resident |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/s1.jpg">chief</A> |
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<A HREF="https://nms.kcl.ac.uk/christian.urban/s2.jpg">paleontologist</A>. |
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</TD> |
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<B>Nominal Isabelle</B> |
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I am the main developer of 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://www21.in.tum.de/~berghofe/">Dr Stefan Berghofer</A>, |
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<A HREF="http://sketis.net/">Dr Markus Wenzel</A>, |
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<A HREF="http://cl-informatik.uibk.ac.at/users/cek/">Dr Cezary Kaliszyk</A>, |
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<A HREF="http://user.it.uu.se/~tjawe125/">Dr Tjark Weber</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 with this 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="https://www.humboldt-foundation.de">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> in Munich. |
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Between 2006 and 2011 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="https://www.dfg.de/en/research_funding/programmes/individual/emmy_noether/">fellowship</A> at the TUM. |
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There is a <A HREF="https://nms.kcl.ac.uk/christian.urban/Nominal/">webpage</A> about Nominal |
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Isabelle, which 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, CPP, SEFM, |
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the Haskell Symposium and |
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in the Journal of Automated Reasoning. Nowadays, Nominal Isabelle 2 is part of the <A HREF="https://www.isa-afp.org">Archive of Formal Proofs</A>. |
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<B>Real-Time Scheduling and Priority Inheritance</B> |
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In real-time operating systems with processes, resource locking and |
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priority scheduling, one faces the problem of |
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<A HREF="http://en.wikipedia.org/wiki/Priority_inversion">priority inversion</A> (processes |
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with lower priority block processes with higher priority indefinitely). If you do not prevent this problem, |
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then processes can behave erratically, as <A HREF="http://www.nasa.gov">NASA</A> found out the |
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<A HREF="http://catless.ncl.ac.uk/Risks/19.54.html#subj6">hard</A> way with their first |
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<A HREF="http://www.nasa.gov/mission_pages/mars-pathfinder/index.html">Mars Pathfinder mission</A>. |
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The priority inheritance protocol is a widely used scheduling algorithm that prevents |
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priority inversion. However, the <A HREF="http://dx.doi.org/10.1109/12.57058">original paper</A> |
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describing this algorithm contains an incorrect algorithm and a bogus(!) correctness proof. |
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We formalised our version of the priority inheritance protocol, including a generalisation |
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of the original work (we allow overlapping critical sections) in the theorem prover |
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<A HREF="http://isabelle.in.tum.de">Isabelle</A>. |
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In our formalisation we use the inductive method we learned from |
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<A HREF="https://www.cl.cam.ac.uk/~lp15/">Prof. Larry Paulson</A>. |
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He used this method in order to prove the correctness of cryptographic |
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protocols. We have implemented our algorithm on top of the |
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the small <A HREF="https://en.wikipedia.org/wiki/Pintos">PINTOS</A> |
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operating system used for teaching (we passed all their test cases and were |
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faster than their reference implementation). |
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While the problem with the original algorithm was already known for some time, the incorrect |
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specification seems to be still widely in use and described in many textbooks on real-time operating systems, |
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including famous and rather expensive |
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ones. Feel free to decide whether they are worth your time and money. Task: Spot the problems in |
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<A href="https://www.amazon.com/Real-Time-Systems-Design-Analysis-Practitioner-ebook/dp/B0062LNOCW">here</A>, |
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<A href="https://www.amazon.co.uk/Real-Time-Concepts-Embedded-Systems-Qing/dp/1578201241">here</A>, |
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<A href="https://www.amazon.co.uk/Real-Time-Systems-Jane-W-Liu/dp/0130996513">here</A>, |
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<A href="https://www.springer.com/gp/book/9780792392118">here</A> and |
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<A href="https://www.os-book.com/OS9/">here</A>! |
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Alternatively, you can look at the quotes and pointers in our |
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<A HREF="http://nms.kcl.ac.uk/christian.urban/Publications/pip.pdf">paper</A>. A notable |
|
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exception is the <A HREF="https://www.springer.com/gp/book/9781461406754">textbook</A> |
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by Buttazzo, who gives the correct specification. Unfortunately, his work did not |
|
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help us with proving the correctness of the priority inheritance protocol. |
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This is joint work with Prof. Xingyuan Zhang and his student Chunhan Wu from the |
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PLA University of Science and Technology in Nanjing. |
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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 reasoning in theorem provers with worn-out examples like |
| 2 | 290 |
fib and even/odd, we implemented a large part of regular language theory in Isabelle/HOL. |
291 |
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.pdf">here</A> and |
| 2 | 294 |
<A HREF="http://ropas.snu.ac.kr/~kwang/paper/06-jfp-yi.pdf">here</A>. It turns out that |
295 |
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 based on HOL. |
| 2 | 298 |
We therefore went against the |
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<A HREF="http://www.cs.cornell.edu/~kozen/papers/papers_by_year.htm#K97a">mainstream</A> |
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and used in our formalisation regular expressions exclusively, |
301 |
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 |
|
304 |
result about Subseq, which according to |
|
305 |
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. We also answered a |
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<A HREF="http://blog.computationalcomplexity.org/2013/02/proving-dfa-langs-closed-under-concat.html">question</A> from the same blog about |
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"proving Reg-exp-langs [being] closed under complementation without using equiv to DFA's"....yes we can! |
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This is joint work with Prof. Xingyuan |
| 2 | 311 |
Zhang and his student Chunhan Wu from the |
| 592 | 312 |
PLA University of Science and Technology in Nanjing. |
| 2 | 313 |
My funding for this work came from the |
| 587 | 314 |
<A HREF="http://sinogermanscience.dfg.nsfc.cn/de/index.html">Chinese-German Research Centre</A>. |
| 2 | 315 |
</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="https://nms.kcl.ac.uk/christian.urban/Unification">Nominal unification</A> is one outcome of |
| 2 | 322 |
my involvement in the nominal logic project in Cambridge. Another is the logic programming language |
323 |
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 |
|
325 |
<A HREF="http://homepages.inf.ed.ac.uk/jcheney/programs/aprolog/">here</A>. |
|
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The nominal unification algorithm has been |
|
| 519 | 327 |
<A HREF="https://nms.kcl.ac.uk/christian.urban/Unification">formally verified</A> in Isabelle. This |
| 2 | 328 |
was possible since this unification algorithm is formulated in a simple first-order language |
329 |
(unlike other algorithms for higher-order unification). |
|
| 466 | 330 |
<A HREF="https://nms.kcl.ac.uk/maribel.fernandez/">Prof. Maribel Fernandez</A> and her student |
| 2 | 331 |
improved the nominal unification algorithm to be quadratic. |
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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. This work has also found its |
|
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parents:
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way into <A HREF="http://clojure.org">Clojure</A> as the <A HREF="https://github.com/clojure/core.logic/wiki/core.logic.nominal">core.logic.nominal</A> package. |
| 2 | 335 |
My funding for this work was provided through a research fellowship from |
336 |
<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> |
|
345 |
and for three years |
|
346 |
called Gonville and Caius College my home. I was very lucky to have |
|
| 362 | 347 |
<A HREF="https://labs.oracle.com/pls/apex/f?p=labs:bio:0:2044">Dr Gavin Bierman</A> |
| 2 | 348 |
as supervisor. My research in Cambridge was also very much influenced by |
349 |
<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 |
|
| 519 | 351 |
<A HREF="https://nms.kcl.ac.uk/christian.urban/PhD/index.html">elsewhere</A>, including |
352 |
a <A HREF="https://nms.kcl.ac.uk/christian.urban/Cut/cutapplet.html">Java Applet</A> that |
|
| 2 | 353 |
'visualises' some of the results from the thesis. I completed the writing of |
354 |
the thesis in <A HREF="http://iml.univ-mrs.fr/ldp/">Marseille</A> in the group of |
|
| 588 | 355 |
<A HREF="http://girard.perso.math.cnrs.fr/Accueil.html">Prof. Jean-Yves Girard</A>. My study in |
| 2 | 356 |
Cambridge was funded by two <A HREF="http://www.daad.de/index.html">scholarships</a> |
357 |
from the German government; my year in Marseille by a TMR-fellowship from the EU. |
|
358 |
My PhD was also one starting point for the EPSRC Project on the Semantics of Classical |
|
| 64 | 359 |
Proofs. The strong normalisation result in the PhD has been used in 2007 by |
| 616 | 360 |
<A HREF="https://jao2015.sciencesconf.org/conference/jao2015/pages/Claude_Kirchner.pdf">Prof. Claude Kirchner</A> and his |
| 66 | 361 |
students for proving consistency of their superdeduction system lemuridae. |
| 2 | 362 |
</TD> |
363 |
</TR> |
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<TR> |
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<TD BGCOLOR="#FFFFFF" WIDTH="75%"> |
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<B>Forum</B> |
|
370 |
I implemented Forum, a programming language based on classical linear logic, |
|
371 |
as my M.Phil. thesis. This was joint work with |
|
| 616 | 372 |
<A HREF="https://st-andrews.academia.edu/RoyDyckhoff">Dr Roy Dyckhoff</A>. |
| 2 | 373 |
Details can be found |
| 469 | 374 |
<A HREF="https://rd.host.cs.st-andrews.ac.uk/logic/nonmac/">here</A> and |
| 2 | 375 |
<A HREF="http://www.lix.polytechnique.fr/Labo/Dale.Miller/forum/">here</A>. During my |
376 |
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 |
|
| 519 | 384 |
<A HREF="https://nms.kcl.ac.uk/christian.urban/Prover/index.html">here</A>. |
| 67 | 385 |
<A HREF="http://pizzacompiler.sourceforge.net">Pizza</A>, written around 1996, is a conservative |
| 69 | 386 |
extension of Java and a precursor of Scala. My implementation illustrates the technique of |
| 604 | 387 |
success continuations in proof search. <B>Update:</B> This ancient work inspired |
| 603 | 388 |
<A HREF="http://rosien.net/">Adam Rosien</A> to re-surrect some parts of it in |
| 605 | 389 |
<A HREF="https://github.com/arosien/sequentish/blob/master/src/main/scala/net/rosien/sequentish/LJT.scala">Scala</A> [<A HREF="https://github.com/arosien/sequentish">github</A>, |
390 |
<A HREF="https://arosien.github.io/sequentish/slides.html#/">slides</A>] |
|
| 2 | 391 |
</TD> |
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</TR> |
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</TABLE> |
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<P> |
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<a href="https://validator.w3.org/check/referer">[Validate this page.]</a> |
| 591 | 398 |
</font> |
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