Friday, December 03, 2010

Pushdown Automata and Vector Addition Systems

Philippe Schnoebelen just sent me an email announcing the forthcoming event Pushdown Automata and Vector Addition Systems: A New Look At Two Classical Problems, which will be held at LSV in Cachan on January 20, 2011.Quoting from the web page for this one-day event:
This special event focuses on two recent major claims/results:
  • a new proof, by P. Jančar, for the decidability of equivalence for deterministic pushdown automata, first established by G. Sénizergues, and
  • a new proof, by J. Leroux, for the decidability of accessibility in vector addition systems, or equivalently in Petri nets, first established by E. Mayr (and S. R. Kosaraju).
Our aim here is to provide an exceptional opportunity for Jančar and Leroux to provide an in-depth presentation of their proofs in front of a large audience of expert specialists as well as younger researchers interested in the field. This will be a unique occasion for the kind of interaction and attention to details that is only possible in a 3-hour tutorial format.
This sounds like a very interesting event. If you happen to be in Paris at around that time, do make a point of attending it. For those of us who cannot be there,  Jančar and Leroux have posted write-ups of their results here and here.

Tuesday, November 02, 2010

Springer's LNCS

Over the last few days, I have been exchanging emails with the chief librarian at my university to find out how much Springer charges us for access to its LNCS proceedings series. My enquiries were prompted by some remarks from a colleague from outside Iceland who told me that her library will likely stop subscribing to LNCS starting in 2011.  

Yesterday, my contact at our library wrote to me saying that LNCS is not part of the Icelandic National Licence to Springer journals, SpringerLINK. Our library used to buy it as a special subscription and we had a deal with Springer for a three year period. This subscription was one of the special subscriptions we had to cancel after the financial crisis. She also told me that the subscription fee for access to LNCS for the year 2009 was the "special price" of  7.566,00 EUROS. (I wonder what the standard price is.) 

I wonder whether your library will continue subscribing to LNCS. (Do post a comment if you have any information on this!) Times are hard for everyone, or so it seems, and perhaps university libraries are becoming more selective in choosing what journals and proceedings series they subscribe to. 

Friday, October 29, 2010

Call for nominations for EATCS awards

The calls for nominations for the EATCS Award, the Presburger Award and the Gödel Prize for 2011 are now out. See here for details. The deadlines are approaching fast, so get your nominations ready now!

Wednesday, October 20, 2010

Postdoctoral position at Reykjavik University

Processes and Modal Logics

School of Computer Science, Reykjavik University

One postdoctoral position

Applications are invited for one postdoctoral position at the School of Computer Science, Reykjavik University.  The position is part of a research project funded by the Icelandic Fund for Research, under the direction of Anna Ingolfsdottir and Luca Aceto. The general aim of the project is to contribute further advances to the study of the connections between the theory of reactive systems, modal logics and logics of knowledge, amongst others. See the web page of the project at

for more details on the project.

The successful candidates will benefit from, and contribute to, the research environment at the Icelandic Centre of Excellence in Theoretical Computer Science (ICE-TCS). For information about ICE-TCS and its activities, see

Qualification requirements

Applicants for the postdoctoral position should have a PhD degree in Computer Science, Mathematics or closely related fields. Previous knowledge of at least one of concurrency theory, modal/epistemic logics and their applications in computer science, and process calculi is highly desirable.


The wage is 330,000 ISK (roughly 2,120 euros at the present exchange rate) per month before taxes. The position is for one year, starting in January 2011 or as soon as possible thereafter, and is renewable for another year, based on good performance and mutual satisfaction.

Application details

Interested applicants should send their CV, including a list of publications, in PDF to the addresses below, together with a statement outlining their suitability for the project and the names of two referees.

Anna Ingolfsdottir

Luca Aceto

We will start reviewing applications as soon as they arrive, and will continue to accept applications until the position is filled.

Wednesday, October 06, 2010

LICS 2011 Test-of-Time Award Nominations

The LICS Test-of-Time Award recognizes a small number of papers from the LICS proceedings from 20 years prior that have best met the "test of time". The LICS 2011 Test-of-Time Award committee is, as usual, stellar and consists of Tom Henzinger, Radha Jagadeesan, Catuscia Palamidessi, and Andy Pitts (Chair). All papers published in the LICS 1991 Proceedings are eligible, see here for the complete list. Any member of the LICS community is welcome to send recommendations to Andy Pitts at

I already sent in my nomination yesterday, and I encourage my readers to recommend their favourite paper from LICS 1991. This is my fourth nomination this year, and so far I am zero out of three. Let's see whether the author of the paper I recommended will be any luckier.

Wednesday, September 29, 2010

Call for Papers for FSEN 2011

I have been asked to distribute this call for papers. Consider submitting to FSEN 2011, thereby supporting a young, good-quality conference in formal approaches to software engineering, broadly construed!

                         CALL FOR PAPERS

                   Fourth International Conference on
               Fundamentals of Software Engineering 2011
                        Theory and Practice
                               (FSEN '11)


                            Tehran, Iran
                          April 20-22, 2011


About FSEN

FSEN is an international conference that aims to bring together
researchers, engineers, developers, and practitioners from the academia
and the industry, who work in every area of formal methods. This
conference seeks to facilitate the transfer of experience, adaptation of
methods, and where possible, foster collaboration among different groups.
The topics of interest cover all aspects of formal methods, especially
those related to advancing the application of formal methods in the
software industry and promoting their integration with practical
engineering techniques. Following the success of the previous FSEN events
in 2005, 2007 and 2009, the next event in the FSEN series will take place
in Tehran, Iran, April 20-22, 2011.

In cooperation with


Important Dates

Abstract Submission:   October 18 , 2010
Paper Submission:      October 25 , 2010
Notification:          December 13, 2010
Camera Ready:          January 10 , 2011
Conference:            April 20-22, 2011

Keynote Speakers

Carlo Ghezzi, Politecnico di Milano, Italy
Joost-Pieter Katoen, RWTH Aachen University, Germany

(Third speaker to be announced)

Topics of Interest

The topics of this symposium include, but are not restricted to, the

* Models of programs and systems
* Software specification, validation and verification
* Software architectures and their description languages
* Object and multi-agent systems
* Coordination and feature interaction
* Integration of formal and informal methods
* Integration of different formal methods
* Component-based development
* Service-oriented development
* Model checking and theorem proving
* Software and hardware verification
* CASE tools and tool integration
* Application to industrial cases

The length of each paper including figures and references must not exceed
15 pages and should conform to the Springer LNCS style. All papers must be
submitted in PDF or postscript format. Submissions should explicitly state
their contribution and their relevance to the theme of the conference.
Other criteria for selection will be originality, significance,
correctness, and clarity. Simultaneous or similar submissions to other
conferences or journals are not allowed.

Proceeding and Special Issues

The post-proceedings of FSEN11 will be published by Springer Verlag in the
LNCS series.  There will also be a pre-proceeding for the accepted papers,
which is printed locally by IPM. This pre-proceeding will be made
available at the conference.

The proceedings of FSEN07 and FSEN09 were published in the LNCS series. A
special issue of Science of Computer Programming is being published,
containing the extended versions of a selection of papers of FSEN09. A
special issue of Fundamenta Informaticae was published, containing the
extended versions of a selection of papers of FSEN07. The proceedings of
FSEN05 was published in the ENTCS series: ENTCS 159 (2006). Two special
issues were published containing the extended versions of a selection of
papers of FSEN05 in Fundamenta Informaticae (FI, vol. 82, 2008) and  in
Journal of Universal Computing (J.UCS, 13(13), 2007).

General Chair

Hamid Sarbazi-azad - IPM, Iran; Sharif University of Technology, Iran

Program Chairs

Farhad Arbab - CWI, Netherlands; Leiden University, Netherlands
Marjan Sirjani - Reykjavik University, Iceland; University of Tehran, Iran

Steering Committee

Farhad Arbab - CWI, Netherlands; Leiden University, Netherlands
Christel Baier - University of Dresden, Germany
Frank de Boer - CWI, Netherlands; Leiden University, Netherlands
Ali Movaghar - IPM, Iran; Sharif University of Technology, Iran
Hamid Sarbazi-azad - IPM, Iran; Sharif University of Technology, Iran
Marjan Sirjani - Reykjavik University, Iceland; University of Tehran, Iran
Jan Rutten - CWI, Netherlands; Vrije University Amsterdam, Netherlands

Program Committee

Luca Aceto - Reykjavik University, Reykjavik, Iceland
Gul Agha - University of Illinois at Urbana - Champaign, USA
Farhad Arbab - CWI, Netherlands; Leiden University, Netherlands
Jos Baeten - Eindhoven University of Technology, Netherlands
Christel Baier - University of Dresden, Germany
Frank de Boer - CWI, Netherlands; Leiden University, Netherlands
Marcello Bonsangue - Leiden University, Netherlands
Mario Bravetti - University of Bologna
James C. Browne - University of Texas at Austin, USA
Einar Broch Johnsen - University of Oslo, Norway
Michael Butler - University of Southampton, UK
David Clarke - CWI, Netherlands; K.U.Leuven, Belgium
Wan Fokkink - Vrije Universiteit Amsterdam, Netherlands
Masahiro Fujita - University of Tokyo, Japan
Maurizio Gabbrielli - University of Bologna, Italy
Radu Grosu - State University of New York at Stony Brook, USA
Jan Friso Groote - Technical University of Eindhoven, Netherlands
Joost Kok - Leiden University, Netherlands
Ramtin Khosravi - University of Tehran, Iran
Kim Larsen - Aalborg University, Denmark
Zhiming Liu - United Nations University, Macao, China
Seyyed Hassan Mirian - Sharif University of Technology, Iran
Sun Meng - Peking University, China
Ugo Montanari - University of Pisa, Italy
Peter Mosses - Swansea University, UK
Mohammad Reza Mousavi - Technical University of Eindhoven, Netherlands
Ali Movaghar - IPM, Iran; Sharif University of Technology, Iran
Andrea Omicini - University of Bologna, Italy
Saeed Parsa - Iran University of Science & Technology, Iran
Hiren Patel - University of Waterloo, Canada
Jan Rutten - CWI, Netherlands; Vrije University Amsterdam, Netherlands
Davide Sangiorgi - University of Bologna, Italy
Marjan Sirjani - Reykjavik University, Iceland; University of Tehran, Iran
Carolyn Talcott - SRI International, USA

Tuesday, September 21, 2010

CNRS Bronze Medal to Thomas Colcombet

Thomas Colcombet of LIAFA, Université Paris Diderot - Paris 7, has been awarded a CNRS bronze medal. See here for the full list of awardees. As you can see, Thomas is the only recipient of the award in the field of computer science. It is good for TCS at large to see one of its researchers receive such a prestigious national award.

This has been quite a year for researchers working on the classic theory of automata, logic and their applications. Earlier in 2010, one of Thomas' collaborators, viz. Mikolaj Bojanczyk, received the first Presburger Award and Anca Muscholl was awarded a CNRS silver medal.

Congrats to all of them!

Thursday, September 09, 2010

SOS 2010

On August 30, Pawel Sobocinski and I co-chaired SOS 2010, an affiliated workshop of CONCUR 2010. The workshop programme was interesting and we had 18 participants. (It was hard to compete with EXPRESS 2010, which had 35 registered participants.) The proceedings for the workshop are available as an EPTCS volume.

Apart from five contributed talks touching on a fairly wide variety of topics, the workshop featured two invited presentations. MohammadReza Mousavi kicked off the workshop in style with a talk entitled How to cook a security-enabled semantics. In his talk, which was partly based on this paper, Mohammad introduced notions such as restricted revocable delegation and studied their consequences in language-based security. Listening to Mohammad speak I felt, not for the first time, that language-based security is one of the (alas, many) topics that I should make an effort to understand better.

The second invited talk was joint with EXPRESS, and was delivered by Catuscia Palamidessi. Catuscia had a very large audience for a workshop, and fortunately we had decided to move to a lecture hall that could hold about 100 people before her talk :-). Catsucia's talk, which was entitled Compositionality of Secure Information Flow, dealt with ways in which one can quantify the amount of leakage of confidential information through public outputs in computer systems. Catuscia discussed a proposal for measuring the amount of leakage that is based on the Bayes risk, namely (the converse of) the probability of guessing the right value of the secret, once we have observed the output. In her talk, Catuscia presented a process calculus for the specification of systems composed by concurrent and probabilistic processes, and investigated "safe constructs", namely constructs which do not increase the leakage.

Overall, I like to think that SOS 2010 was a successful workshop. However, I would like to see this workshop series be more visible and receive more submissions. I hope that future chairs will be more successful than I have been in achieving these goals.

Wednesday, September 08, 2010

A Selection of Papers from CONCUR 2010

As I have already mentioned in earlier posts, I enjoyed a lot of talks in the programme for CONCUR 2010. Here are just a few highlights, with apologies to all the speakers whose talks/papers I do not mention in this post. Overall, the conference programme was of very high quality. This bodes well for the future of CONCUR.
  • Lutz Schröder and Yde Venema. Flat Coalgebraic Fixed Point Logic. Lutz presented the paper and gave a very clear introduction to the coalgebraic approach to the study of modal logics. Technically, this paper presents a unified co-algebraic treatment  of flat fixed-point logics. (Fixed-point logics, such as the mu-calculus, are widely used in computer science, in particular in artificial intelligence and concurrency.) The main results in the paper are the completeness of the Kozen-Park axiomatization and a general  EXPTIME upper bound for flat fixed-point logics.
  • Fides Aarts and Frits Vaandrager. Learning I/O Automata. The talk was delivered by Frits, who addressed the general question of learning models of reactive systems automatically, e.g., for model-based testing or software engineering.In this work, Fides and Frits establish links between three widely used modelling frameworks for reactive systems: the ioco theory of Tretmans, the interface automata of De Alfaro and Henzinger, and Mealy machines. It is shown that, by exploiting these links, any tool for active learning of Mealy machines can be used for learning I/O automata that are deterministic and output determined. The approach presented in the paper has been implemented on top of the LearnLib tool and has been applied successfully to three case studies, including learning a model of Fides' biometric passport
  • Pawel Sobocinski. Representations of Petri net interactions. Pawel, who was my co-chair for SOS 2010, presented a novel compositional algebra of Petri nets. The algebra contains two binary operators (tensor product and sequential composition) and twelve constants! He also introduced a stateful extension of the calculus of connectors and showed that .these two formalisms have the same expressive power.
  • Pavol Cerny, Thomas Henzinger and Arjun Radhakrishna. Simulation Distances The simulation preorder is often used to establish the correctness of an implementation I with respect to a specification S as follows: I correctly implements S if S can simulate the behaviour of I. In other words, this happens if everything the implementation I does is allowed by the specification S. The result of such a verification is boolean and cannot be used to assess how far I is from implementing the behaviour allowed by  S. This paper extends the simulation preorder to the quantitative setting by  defining three different simulation distances. The correctness distance measures how much the specification must be changed in order to be satisfied by the implementation. The coverage distance measures how much the implementation restricts the degrees of freedom offered by the specification. The robustness distance measures how much a system can deviate from the implementation description without violating the specification. The paper develops a comprehensive theory for those notions of simulation distances. 
Reading the papers from CONCUR 2010 will keep me busy for some time. 

    Tuesday, September 07, 2010

    Milner Session at CONCUR 2010

    During CONCUR 2010, the concurrency-theory community paid a small tribute to Robin Milner by dedicating a session of its flagship conference to him. The so-called Milner Session was held on Wednesday, 1 September, from 2pm till 4pm. It consisted of a talk by Jos Baeten and of three presentations of papers that were selected for the conference by the PC.

    Jos kicked off the session with a talk devoted to Milner's contributions to concurrency theory. He focused on his seminal Calculus of Communicating Systems, providing an overview of its syntax, of some of the design decisions Milner made in that calculus and of its semantics. The presentation by Jos was followed by a short discussion, with remarks from Ugo Montanari, Kohei Honda and myself, amongst others.

    My two readers might be interested in reading a short note  by Samson Ambramsky entitled Robin Milner's Work on Concurrency that was published yesterday in the Proceedings of MFPS 2010. According to Samson,
    Robin’s ideas have become part of the air we breathe in our scientific community.....

    CCS was not just a new calculus, but a new paradigm — that has played a central role in the subsequent development of our subject. It opened up the world of compositional behavioural modelling.
    I have always found that one of the red threads in Milner's work was the, I believe novel, emphasis on behavioural semantics and on his standpoint that a process is an equivalence class of process descriptions (be they terms in a process algebra/calculus or states in a labelled transition system/automaton) modulo some notion of behavioural equivalence. Milner himself reiterated this point in several of his writings/talks, and I am glad to see this mentioned in Samson's piece.
    We knew what functions were already! But what are processes? CCS established the fundamental methodological point of studying them through their observational behaviour (defined in terms of labelled transition systems via SOS).

    This led inexorably in turn to notions of observational equivalence.
    Thanks to Jos and Samson for their tributes to Milner's work.

    Amongst the contributed talks in the Milner Session, let me mention the excellent talk by Edsko de Vries, who presented joint work with Vasileios Koutavas and Matthew Hennessy on Communicating Transactions. Communicating transactions are obtained by dropping the isolation requirement from standard transactions and can be used to model automatic error recovery in distributed systems. Edsko presented a behavioural theory for a version of CCS with communicating transactions that  is sound and complete with respect to the may-testing preorder. The technical work looked really impressive.

    I really enjoyed Silvia Crafa's talk entitled A Logic for True Concurrency, which presented joint work with Paolo Baldan. Perhaps, I was biased since Silvia's talk brought me back in time some twenty years, when a different version of myself was working on topics related to true concurrency. However, I was not the only one to be impressed by that paper, which proposes a logic for true concurrency whose formulae describe events in computations and their causal dependencies. The induced logical equivalence is hereditary history preserving bisimilarity. The authors also identify fragments of the logic that capture other truly concurrent behavioural equivalences in the literature: step, pomset and history preserving bisimilarity. After Silvia's talk, I felt that her paper with Paolo should have been written long ago. 

    Monday, September 06, 2010

    A Thought Experiment

    Suppose that a top-class conference to which you usually submit your papers decide to publish its proceedings in an electronic open-access outlet instead of using a commercial publisher, like STACS and FST-TCS have done over the last few years. Would that decision have any effect on whether you submit your papers to that conference? Would you encourage your students to submit to that conference in order to further their future career? Do you think that a prestigious conference has anything to lose in publishing its proceedings in an electronic open-access outlet?

    Sunday, September 05, 2010

    CONCUR 2010

    From August 30 till the very early hours of September 3, I was in Paris to co-chair SOS 2010 and attend CONCUR 2010. It is always a pleasure to have the chance to attend CONCUR, which is the flagship conference for the concurrency-theory community, and the lure of Paris made this conference even more attractive than usual.

    CONCUR 2010 was perfectly organized by Paul Gastin (LSV, ENS Cachan, France), François Laroussinie (LIAFA, Université Denis Diderot - Paris 7, France) and their support team (see the bottom of this page for the details), and was held at Université Denis Diderot - Paris 7.

    According to the program chairs, there were 160 people registered for the main conference and 215 people were registered for the conference or one of the eight affiliated events. I am not a CONCUR historian, but I believe that this makes this edition of CONCUR one of the best attended on record, together with the one held in Bologna last year. I do not find this level of attendance particularly surprising----after all, Paris is an attractive city and it is one of the hotbeds of research in concurrency theory. However, it is a great credit to the organizational effort that everything went smoothly and that the atmosphere at the conference was relaxed and conducive to both scientific and social exchanges.

    On behalf of the CONCUR community, I'd like to say thanks to François, Paul and their support team for organizing a great conference. We had many excellent talks on a variety of exciting topics, a session devoted to Robin Milner (chaired by Matthew Hennessy and featuring a talk by Jos Baeten), varied and tasty lunches served next to the conference room, and yet another edition of the CONCUR football match (which saw about 20 participants kick a ball around for about one hour before the conference dinner).

    I hope to devote another post to the main conference and to SOS 2010. Here I will just limit myself to a few brief remarks on the invited talks that I could attend. (Unfortunately, I had to leave at an ungodly early hour on Friday, 3 September, and therefore I missed  Holger Hermann's invited presentation and the last day of the conference. Knowing Holger's communication skills, I am sure that I missed a great talk. I hope that Holger will make a recording of his talk available from his web page.)

    The conference was given the best possible start by Vladimiro Sassone, who delivered a very clear talk entitled Trust in Anonymity Networks.  In his presentation, after having introduced the basic setting of anonymity protocols, Vladimiro presented an analysis of the privacy guarantees of the Crowds anonymity protocol, with and without onion forwarding, for standard and adaptive attacks against the trust level of honest users.

    I had the great honour of chairing the session featuring the second invited talks, which was delivered by Maurice Herlihy. After-lunch sessions are always challenging, especially when the conference is held in France, but Maurice's talk, entitled Applications of Shellable Complexes to Distributed Computing, was the perfect digestive after an excellent lunch. In his talk, Maurice reviewed some of the ideas behind his award-winning application of tools from algebraic topology to distributed computing and then discussed some very recent results that will be presented at DISC 2010 in the paper Concurrent Computing and Shellable Complexes co-authored with Sergio Rajsbaum.

    In her talk Taming Distributed Asynchronous Systems, Anca Muscholl delivered a good overview of many results and open problems related to  analysis techniques for distributed, asynchronous systems with two kinds of synchronization, namely shared variables and fifo channels. Anca has just received the prestigious CNRS silver medal for 2010 for computer science. Congrats to her!

    The last invited talk I was able to attend was delivered by Frank S. de Boer, who gave a presentation entitled Dating Concurrent Objects: Real-Time Modeling and Schedulability Analysis. After giving the audience an overview of the CREDO project, Frank introduced a real-time extension of the concurrent object-oriented language Creol, and showed us how to analyze schedulability of an abstraction of real-time concurrent objects in terms of timed automata. He concluded the talk by telling the audience about techniques for testing the conformance between these behavioral abstractions and the executable semantics of Real-Time Creol in Real-Time Maude. I enjoyed the talk, and I think that Frank was successful in keeping his audience away from their laptops and in making the attendees resist the temptation of checking their email during his talk, which was one of his stated aims!

    Addendum.  Holger Hermann's invited presentation is now available (in flash) from here. Enjoy!

    Tuesday, August 24, 2010

    One year of Electronic Proceedings in Theoretical Computer Science (EPTCS)

    Electronic Proceedings in Theoretical Computer Science (EPTCS) was launched by Rob van Glabbeek in 2009, as an initiative to have proceedings of all worthy workshops in Theoretical Computer Science freely available on-line. The papers in the proceedings are simply entries in the CoRR repository. DOI numbers are assigned to EPTCS publications, and they are indexed in CrossRef and in the Directory of Open Access Journals.  There is no charge for authors or workshops/conferences.

    The idea caught on like wildfire, and since EPTCS was launched over 30 proceedings were published, and 22 more have been accepted for publication.

    Perhaps one of the reasons is that the procedure for submitting a proposal is very simple, and our response time to a proposal is very fast, usually less than 10 days. Additionally, thanks to efficient workflow, proceedings usually appear within 10 days after all the constituents have been delivered.

    We find that it is very important to properly record workshop proceedings in one, easily searchable place. Also, we want to contribute in this way to the growing acceptance of the view that all scientific publications should be freely available on-line.

    We hope that researchers working in Theoretical Computer Science will follow the example of the many others in accord with the originators of this idea.  Please see for the list of published workshops.

    The editors,

    Rob van Glabbeek (NICTA, Sydney, Australia)
       Editor in Chief
    Luca Aceto (Reykjavik University)
    Rajeev Alur (University of Pennsylvania)
    Krzysztof R. Apt (CWI and University of Amsterdam)
    Lars Arge (Aarhus University)
    Ran Canetti (Tel Aviv University)
    Luca Cardelli (Microsoft Research)
    Rocco De Nicola (Universita di Firenze)
    Jose Luiz Fiadeiro (University of Leicester)
    Wan Fokkink  (Vrije Universiteit Amsterdam)
    Lane A. Hemaspaandra (University of Rochester)
    Matthew Hennessy (Trinity College Dublin)
    Bartek Klin (Warsaw University, University of Cambridge)
    Evangelos Kranakis (Carleton University)
    Shay Kutten (Technion)
    Nancy Lynch (Massachusetts Institute of Technology)
    Aart Middeldorp (University of Innsbruck)
    Benjamin Pierce (University of Pennsylvania)
    Gordon Plotkin (University of Edinburgh)
    Vladimiro Sassone (University of Southampton)
    Robert H. Sloan (University of Illinois at Chicago)
    Wolfgang Thomas (RWTH Aachen University)
    Irek Ulidowski (University of Leicester)
    Dorothea Wagner (Universitaet Karlsruhe (TH))
    Martin Wirsing (LMU Munich)
    Moti Yung (Google Inc. and Columbia University)

    Thursday, August 19, 2010

    Rolf Nevanlinna Prize to Daniel Spielman

    Daniel Spielman  has been chosen for the 2010 Rolf Nevanlinna Prize for smoothed analysis of Linear Programming, algorithms for graph-based codes and applications of graph theory to Numerical Computing. The full details are here.

    Congrats to Daniel for landing another prize after the Goedel prize 2008, which he received in Reykjavik during ICALP 2008.

    Details about the other prize winners are here.

    Wednesday, July 07, 2010

    An interesting publication experiment in the logic-programming community

    Krzysztof Apt has alerted me of the changes that have taken place in the Logic Programming community. The Association for Logic Programming (ALP) recently left the Springer LNCS series and embraced a new publication model for the proceedings of their flagship conference (the International Conference on Logic Programming (ICLP)) that tries to upgrade the papers directly to journal papers. Here is how the co-chairs of the 2010 edition of the conference describe the new publication model and its rationale.

    The Logic Programming (LP) community, through the Association for Logic Programming (ALP) and its Executive Committee, decided to introduce for 2010 important changes in the way the main yearly results in LP and related areas are published. Whereas such results have appeared to date in standalone volumes of proceedings of the yearly International Conferences on Logic Programming (ICLP), and this method – fully in the tradition of Computer Science (CS) – has served the community well, it was felt that an effort needed to be made to achieve a higher level of compatibility with the publishing mechanisms of other fields outside CS.

    In order to achieve this goal without giving up the traditional CS conference format a different model has been adopted starting in 2010 in which the yearly ICLP call for submissions takes the form of a joint call for a) full papers to be considered for publication in a special issue of the journal, and b) shorter technical communications to be considered for publication in a separate, standalone volume, with both kinds of papers being presented by their authors at the conference. Together, the journal special issue and the volume of short technical communications constitute the proceedings of ICLP.

    The special issue of the journal  Theory and Practice of Logic Programming (TPLP) devoted to the 26th International Conference on Logic Programming Special is the first of a series of yearly special issues of that journal putting this new model into practice. It contains the papers accepted from those submitted as full papers (i.e., for TPLP) in the joint ICLP call for 2010. The collection of technical communications for 2010 will appear in turn as Volume 7 of the Leibniz International Proceedings in Informatics (LIPIcs) series, published on line through the Dagstuhl Research Online Publication Server (DROPS). Both sets of papers will be presented by their authors at the 26th ICLP.

    This seems a very interesting way of dealing with some of the concerns that have been aired by some pundits about the publication culture within CS, while preserving the crucial role that conferences play in CS. I think that it is certainly worth a thought.

    Monday, July 05, 2010

    Call for papers: ICALP 2011

    The first call for papers for ICALP 2011, which is presently being distributed at ICALP 2010, is here.

    I hope that you will make plans to submit excellent papers to ICALP 2011.

    Tuesday, June 22, 2010

    Organizing a conference with satellite events

    Suresh asked me to expand on a comment I posted here, where I described my experience with the organization of ICALP 2008 in Reykjavik, which I believe is still the most attended and event-packed ICALP conference on record.

    First of all, even without satellite events, ICALP is a three-track conference, and has been so since 2005, though typically only two tracks are running in parallel at each point in time. At ICALP 2008, in addition we had 12 satellite events, including the DYNAMO training school for doctoral students. There were no tutorials, apart from the lectures at the PhD school, but we hosted a masterclass by Peter Winkler on mathematical puzzles, which I estimate was attended by well over 250 people, including local high-school teachers and students. Overall, nearly 500 people were registered for the main conference and/or the satellite events.

    The workshops were held the day before ICALP or during the week-end following it. They were selected by the ICALP organizers amongst a fairly large number of proposals that we received in response to a call for workshops, based on their perceived scientific quality and on their potential interest to the ICALP community. As ICALP organizers, we made sure that each workshop had a suitable room at the university and some minimal amount of logistical and technical support. (Typically, at least a local student or a postdoc was permanently in residence during each workshop.) We also printed the preliminary proceedings of the workshops and took care of arranging lunches and coffee breaks. The costs were covered by the workshop registration fees. Overall, the overhead generated by the organization of the satellite events was minimal, or at least it looks so two years after the facts :-)

    Organizing such a conference was not an easy job, but it was not as daunting as it may seem. In hindsight, I think that it was important to organize the event at the university (not a hotel---in passing, I very much prefer attending events held at universities rather than hotels), to have the assistance of the university support services, of some local students and postdocs, and of experienced conference organizers who took care of the registrations, of the lunches and coffee breaks and of the social programme. Magnus Halldorsson, Anna Ingolfsdottir and I organized ICALP and were assisted by Bjarni Haldorsson and MohammadReza Mousavi in the organization of the workshops. I firmly believe that the task of organizing a conference like ICALP should be shared amongst several people. This certainly worked for us and helped us work more cheerfully, and overcome personal problems, mishaps and periods of crisis and panic that arose during the year before the conference took place.

    Overall, I do not think that organizing ICALP ended up being much more work than organizing a single-track conference without satellite events.

    Let me close by adding that the model used for ICALP is rather common in conferences related to TCS with a "volume B flavour". See, for instance, the experience of the ETAPS conference series, which involves five major conferences, tutorials and a large number of satellite events, and of the Federated Logic Conference (FLoC), featuring eight major conferences and large number of workshops in 2010. Readers of this post may like to know that typically workshops are proposed by members of the community, and so are the tutorials at ETAPS.

    As an external observer, I fail to see why STOC could not follow the example of those federated conferences and, at the same time, broaden its scope to cover more topics in TCS and accept a few more papers, if their quality is excellent, rather than relinquish its high-profile, peer-reviewed status.

    Wednesday, June 09, 2010

    Gödel Prize 2010

    I have not seen any official announcement yet, but, according to Wikipedia and to Theory Announcements (thanks to the anonymous commenter who pointed out the latter source), the Gödel Prize 2010 has been awarded to Sanjeev Arora and Joe Mitchell for their concurrent discovery of a polynomial-time approximation scheme (PTAS) for the Euclidean Travelling Salesman Problem. Congrats to Arora and Mitchell!

    Friday, May 28, 2010

    Extended Deadlines for SOS 2010

    I am co-chairing SOS 2010, an affiliated workshop of CONCUR 2010, which will be held in Paris. You are still on time to submit a paper to that event! The new submission deadlines are as follows:
    • Submission of abstract: Friday 28th May 2010 Tuesday 1st June 2010 (strict)
    • Submission: Wednesday 2nd June 2010 Monday 7th June 2010 (strict)
    Can you resist the lure of Paris in late August-early September?

    Thursday, May 27, 2010

    My Workplace

    Here are some views of my workplace and its environment. The two photos above picture the entrance to my "professorial work area" :-) The one on the right depicts the entrance to my work area and its immediate environment, with the work places of Anna Ingólfsdóttir (left) and Magnús Halldórsson (right, behind the stand where we place some of our recent papers and books). This is the heart of our ICE-TCS enclave.

    Can one work in such an environment? So far, the answer seems to be yes, but this is mainly because I am starting to believe one can work anywhere provided everyone in one's neighbourhood adheres to some basic ground rules.

    Is the open-space environment conducive to academic work? This I am much less convinced about.

    To conclude, here is what the open-space work environment looks like when I arrive at work in the morning. (The photo is taken from outside my cubicle.)

    First Presburger Award to Mikolaj Bojanczyk

    The Presburger Award Committee, consisting of S. Leonardi, A. Tarlecki, and W. Thomas (chair) has chosen Mikolaj Bojanczyk as the first recipient of the EATCS Presburger Award for young scientists.

    The motivation from the award committee reads as follows:
    Mikolaj Bojanczyk, 32 years old, has contributed numerous deep results to automata theory and to logic and algebra in computer science. Among them is the theorem stating that tree walking automata are strictly weaker than general tree automata, the definition of new decidable logics based on quantifiers for boundedness, and the development of a novel algebraic framework for the study of properties of unranked trees. His work thus led to the solution of long-standing open problems and introduced methods that open new directions in theoretical computer science (also relevant to neighbour disciplines such as data base theory). The committee recommends Mikolaj Bojanczyk as an exceptional young scientist who not only fully deserves the Presburger Award but is also an ideal first recipient. The committee also would like to mention that more than one excellent nomination was made, a fact which lets us hope that the Presburger Award will receive several nominations of truly exceptional level from all areas of theoretical computer science in the coming years.
    Let me add that, in 2005, Mikolaj's doctoral thesis, entitled ”Decidable Properties of Tree Languages”, received the Ackermann award of the European Association of Computer Science Logic. In 2006, he was awarded the ”Witold Lipski prize for young Polish researchers in computer science”. In 2007, he received the Kuratowski award for young Polish mathematicians, awarded by the Polish Mathematical Society. In 2009, Mikolaj became one of the very few young computer scientists to obtain a European Research Council Starting Grant.

    Congrats to Mikolaj for yet another well-deserved award. May his work go from strength to strength.

    Saturday, May 15, 2010

    Fifth International Summer School on Rewriting

    The 5th International School on Rewriting will be held in the period  July 3-8, 2010, in Utrecht, The Netherlands. The programme includes both basic and advanced lectures. Perhaps some of your graduate students will be interested in attending the event.

    Term rewriting is a core area in Theoretical Computer Science. It is powerful model of computation underlying much of declarative programming, which is heavily used in symbolic computation in logic and computer science. Applications can be found in theorem proving and protocol verification, but also in fields as diverse as mathematics, philosophy and biology.


    Monday, May 10, 2010

    School of Computer Science at RU on Twitter

    The School of Computer Science at Reykjavik University, where I work, has made the step to advertise its events and news on Twitter. See here. Our aim is to make potential students and the community at large aware of what the school can offer.

    Does your institution have a Twitter page too? Do you think that Twitter is a good channel for spreading news to potential CS students?

    Thursday, May 06, 2010

    ICE-TCS Logo

    After five years of operation, ICE-TCS (our little research centre in TCS) finally has a logo, which you see displayed above in its full glory. The logo design is courtesy of Emilka Bojańczyk. Do have a look at her graphic design work, which I like a lot. If you need logos, posters or any other kind of TCS- or Maths-related  design work, I strongly recommend Emilka.

    Apart from being a professional graphic designer, Emilka has a mathematical background (she graduated with honours from the Mathematics Department of Warsaw University in 2002) as well as strong family connections with TCS :-) She has also designed the logo for the STACS conference series, amongst other things.

    Thanks Emilka!

    LICS 2010 Test-of-time Award Winners

    I just read an email announcing the papers selected for the 2010 LICS Test-of-Time Award. For the 2010 LICS Test-of-Time Award, all papers from LICS 1990 were considered by an Awards Committee consisting of Glynn Winskel (chair), Jean-Pierre Jouannaud and John Mitchell.

    In view of the weight of highly-influential papers, across a range of areas, the committee has taken the exceptional step of selecting four papers! They are:
    • Model-checking for real-time systems by R. Alur, C. Courcoubetis and D. Dill. This paper was a pioneer in the model checking of real-time systems. It provided a polynomial-space algorithm for the model checking of a real-time logic (an extension of CTL with timing constraints) with respect to a continuous-time model. Its techniques are still used extensively and results of this paper form part of almost any course or tutorial on real-time verification.
    • Symbolic model checking: 10^20 states and beyond by JR Burch, EM Clarke, KL McMillan, DL Dill and LJ Hwang. This paper revolutionized model checking. Through its symbolic representation of the state space using Randy Bryant's Binary Decision Diagrams (BDDs) and its careful analysis of several forms of model checking problems, backed up by empirical results, it provided a first convincing attack on the verification of large-state systems. The paper was a major agent in establishing BDDs as a tool in mainstream computer science.
    • The theory of ground rewrite systems is decidable by M Dauchet and S Tison. This paper asked what has proved to be a very important question, whether the first-order theory of one-step rewriting is decidable. The paper settled the question positively for the theory of ground rewrite systems using innovative techniques on tree automata. Its techniques rekindled an interest in automata theory on finite trees, now a major topic, with many current applications from rewriting through to security, program analysis and concurrency.
    • Recursive types reduced to inductive types by P Freyd. This paper showed what was really going on with the classic method of solving domain equations.  By separating positive and negative occurrences of the unknown in a domain equation, it gave an elegant category-theoretic treatment of recursively defined domains that extends the well-understood and widely-used methods of initial-algebra semantics. Its methods are now standard. They led to new techniques for relating operational and denotational semantics, and new mixed induction/coinduction principles.
    Congratulations to all the recipients of the awards!

    Sunday, April 11, 2010

    Typos, typos....

    I always tell my students at all levels that there is no excuse for not spell checking one's writings. There are rather good spell-checking programs out there, and one should use them to spot obvious typos.

    Spell-checking programs, however, are no substitute for careful proof reading of one's papers. I was reminded of this fact of professional life some time ago when, while reading the revision of a journal submission of mine, I spotted the mention of a "format for impotence of operators" (in lieu of "format for idempotence of operators"). It would have been embarrassing, but admittedly amusing, to send the paper off with that typo left unspotted, just as it was entertaining for my students to attend a lecture mentioning a "poof technique" (rather than "proof technique") on a slide :-)

    No spell-checker can find those typos. I'll use them to motivate my students to proof read their texts with care.

    Thursday, April 08, 2010

    ICALP 2010: Accepted papers

    The list of accepted papers for ICALP 2010 is out. Based on what I saw as a PC member for track B, the overall quality of the submissions was, in general, very high and many good papers could not be selected for presentation at the conference.

    Tuesday, March 30, 2010

    Journal Editors or Black Holes?

    Sometimes journal editors (or referees) are observationally very similar to black holes. A paper is submitted, but no review escapes the force of gravity generated by the scientist in question. If the academic who is submitting the paper is well established, (s)he might not be overly bothered by this "black-hole-like effect" and live to see the day. However, in case the paper is submitted by a young scientist who might be applying for jobs, the negligence of an editor or a reviewer might have negative consequences on the career of the author of the paper.

    Suppose, by way of example, that a young scientist submits a substantial paper to a high-impact journal reporting on the major findings in her doctoral dissertation. The first review round takes a whole year, despite repeated enquiries to the handling editor, and the editor asks for major revisions based on the detailed referee reports. The author works hard at handling the suggestions from her reviewers, and submits a revised paper. One more year passes and the email enquiries by the author receive no answer from the cognizant editor.

    What would be the best line of action for the young scientist in question? Should she wait for a second bunch of reports, which might never come, or would she be best served by withdrawing the paper and submitting it elsewhere? What advice would you give in a situation like this one?

    Saturday, March 27, 2010

    What Are The Hot Research Areas in Concurrency Theory?

    Yesterday Andrei Sabelfeld (Chalmers University of Technology, Sweden) visited ICE-TCS with Arnar Birgisson, a former master student of mine who is now doing doctoral studies under his supervision. Andrei delivered the seminar Information flow in web applications in the ICE-TCS seminar series (the abstract for the talk is here), we talked about liveness and safety properties and about academic matters in general. We at ICE-TCS enjoyed his visit a lot.

    Over dinner,  Andrei asked me:
    • What are the big unsolved problems in concurrency theory?
    • And what are the hot research areas in the field?
    I gave my quarter-baked personal answers, but I'd like to hear yours.

    I have the feeling that research in concurrency theory is driven more by "hot research areas" than by collections of big open problems, but that's just my personal impression, even though at some point I started collecting a list of open problems and stated some in this essay

    Also, how much does the "hotness of a research area" inform the research you do and that you suggest to your students? For what it is worth, for good or for worse, I mostly tend to follow my own personal interests and inclinations rather than the directions of the field at large. However, one  has to "sell" one's work and have it published. It is undoubtedly easier to do so if the work is considered to be hot and timely by a substantial fraction of the research community. Doing work in areas that are considered "important" by many will probably also give a student better opportunities to find further employment.

    Overall, I feel that it is important to give one's students a good problem to work on for her/his dissertation. There are certain characteristics that a good problem should have for sure, but is "hotness" one of those?

    Addendum: There is a lot of good career advice for everyone here.

    Thursday, March 25, 2010

    LICS 2010 Accepted Papers and Martin Grohe's Latest Opus

    The list of accepted papers for LICS 2010 is out. As usual, the programme looks very interesting and exceedingly strong.

    For an interested, but not very knowledgeable, observer like me, one of the most interesting looking papers that have been selected for the conference seems to be yet another seminal contribution by Martin Grohe. The paper is Fixed-Point Definability and Polynomial Time on Graphs with Excluded Minors.

    From the abstract of that ten-page paper, I learn that Grohe proves that fixed-point logic with counting captures polynomial time over all classes of graphs with excluded minors. To my untrained eye, this looks like an amazing result. The proof of this theorem will take up the whole of this monograph, which is currently being written and will be well over 200 pages long. The current draft spans 238 pages.

    Would such a result meet the current requirements for the Gödel prize, say? It seems to me that it would not, unless Grohe also publishes a journal paper based on a fragment of his monograph. Taking the view that proofs of certain results are likely to be very long and that very few journals in computer science would publish papers that are 250 pages long, say, would it not be reasonable to let a research monograph qualify a piece of research for the Gödel prize? After all, if the result is important, it will be studied in depth by many researchers, ensuring a more thorough level of peer review than the one obtained via a standard refereeing process for a journal.

    Monday, March 22, 2010

    The loss of a giant: Robin Milner has passed away

    I just read the following message from Gordon Plotkin. This is really sad news. I plan to post a more elaborate message soon, but we have lost another intellectual giant, a gentleman and a true inspiration for us all.


    Dear Colleagues,

    I am deeply saddened to pass on the following message from Barney and Chloë Milner:

    "We are sorry to announce that Robin Milner died on Saturday 20th March, in Cambridge, just three days after the funeral of his wife, Lucy.

    He will be greatly missed by his family and friends, as well as the academic community."

    Gordon Plotkin

    Friday, March 19, 2010

    SOS 2010

    I am co-chairing SOS 2010 (Structural Operational Semantics 2010) with Pawel Sobocinski (Southampton). The call for papers has been posted on several mailing lists and all the information on this workshop, which is affiliated with CONCUR 2010, is available from the workshop's web site.

    Consider submitting a paper and join us in Paris on August 30 to discuss the latest research on Structural Operational Semantics! I have a series of long-overdue posts describing some of the recent work by my co-authors and me on this topic. I hope to find some time to write those posts after the teaching is over and I have cleared my desk a little.

    Thursday, March 18, 2010

    First Clay Mathematics Institute Millennium Prize Announced Today

    It looks like the Clay Mathematics Institute (CMI) is parting with its first one million USD. Indeed, today the CMI  announced that Grigoriy Perelman is the recipient of the Millennium Prize for the resolution of the Poincaré conjecture. Full details are here and a full-length press release is also available. 

    What do you think will be the next Millennium Prize Problem to fall? It seems very unlikely that it will be our own P vs. NP problem, but, as Bohr taught us,  “Prediction is very difficult, especially about the future".  

    Sunday, February 21, 2010

    Magnús Halldórsson receives the first Reykjavík University Research Award

    This is a belated post on a piece of news that is mostly of local (read, Icelandic) relevance. However, I think that TCS researchers everywhere will be pleased to know that the first research award from Reykjavík University, where I have worked since November 2005, has been given to Magnús M. Halldórsson, for his work on approximation algorithms for computationally hard problems, amongst others. (The announcement in English is here.)  It is good to see the first research award go to a TCS researcher, also because this sets high standards for future such awards.

    It will be interesting to see whether future award committees will be influenced by considerations related to "academic politics" in selecting awardees for the university research award. If not, I expect to see a few awards in the coming years go to people working in (T)CS and combinatorics.

    Belated congratulations to Magnús.

    Sunday, January 24, 2010

    Two PhD Studentships Available

    Yesterday night, I posted the appended announcement of two PhD studentships, which became available thanks to a successful grant application to the Icelandic Fund for Research (Rannis), on a couple of mailing lists.

    I am posting it here too, just in case any of the readers of this blog is interested in applying or has any student who would be a suitable candidate for the studentships.


                Meta-Theory of Algebraic Process Theories

             School of Computer Science, Reykjavik University

              Two PhD studentships

    Applications are invited for two PhD studentships at the School of Computer Science, Reykjavik University.  The positions are part of a three-year research project funded by Rannis (the Icelandic Fund for Research), under the direction of Luca Aceto and Anna Ingolfsdottir.

    Aim of the project

    Algebraic process theories, also known as “process algebras”, are prototype specification languages for reactive systems—that is, for devices that compute by reacting to stimuli from their environment. The main strength of such theories lies in the equational (calculational) style of reasoning they support. For each process theory, several natural questions immediately arise pertaining to the (non-)existence of (finite or recursive) sets of laws that allow one to prove by “substituting equals for equals” all of the valid equalities between process descriptions (closed or open terms) over fragments of the process theory at hand. Currently, answering such questions is only possible via delicate, error-prone and lengthy proofs.

    The aim of the project is to contribute further advances to the study of the meta-theory of algebraic theories of processes.  The main goals of the project are
    • to establish a generic framework for answering questions pertaining to the existence of equational axiomatizations of behavioural semantics over process algebras affording certain desirable properties, such as being finite or recursive, and
    • to apply the proposed general theory to solve some of the main open problems in the study of the equational logic of processes.
    Research environment

    The research  within the project will be carried out in close collaboration with our long-term co-workers Wan Fokkink (VU Amsterdam), Bas Luttik (TU Eindhoven), MohammadReza Mousavi (TU Eindhoven) and Michel Reniers (TU Eindhoven).

    The successful candidates will benefit from, and contribute to, the research environment at the Icelandic Centre of Excellence in Theoretical Computer Science (ICE-TCS). ICE-TCS has currently 14 permanent members, seven postdoctoral researchers and one Ph.D. student.  For more information about ICE-TCS, its members and its activities, see

    Qualification requirements

    Applicants for the PhD studentships should have a good MSc degree in Computer Science, Mathematics or closely related fields, and have a strong background in discrete mathematics and formal systems. Some previous knowledge of topics from at least one of concurrency theory, process calculi and structural operational semantics is not a prerequisite, but would be desirable.


    PhD position: 265,000 ISK (roughly 1,550 euros) per month before taxes, for three years, starting as early as possible and no later than October 2010.

    Application details

    By Friday, 26 February 2010, interested applicants should send their CV, including a list of publications where applicable, in PDF to the addresses below, together with a transcript of their academic record, a statement outlining their suitability for the project and the names of two referees.

    Luca Aceto

    Anna Ingolfsdottir

    We will start reviewing applications as soon as they arrive, and will continue to accept applications until the positions are filled. However, we strongly encourage interested applicants to send in their applications as soon as possible.

    About the School of Computer Science at Reykjavik University

    The School of Computer Science at RU ( has approximately 440 students at the undergraduate, masters and doctorate levels. The School is home to several strong research groups and the main research areas are algorithmics, artificial intelligence, combinatorics, concurrency theory, databases, human-computer interaction, natural language processing, software engineering, theoretical computer science and virtual environments.

    The School of Computer Science at Reykjavik University  has ties with several leading foreign universities, facilitating collaboration, as well as faculty and student exchanges. In particular, the School has a joint M.Sc. degree in Computer Science with the University of Camerino, Italy, and a joint Ph.D. degree programme with KTH, Stockholm, Sweden.

    Information about Ph.D. studies at the School of Computer Science is available at

    Sunday, January 17, 2010

    Concurrency Column for the February 2010 Issue of the BEATCS

    I have just posted the paper for the concurrency column that will appear in the February 2010 Issue of the BEATCS. This installment of the concurrency column is devoted to a very informative survey, contributed by François Laroussinie, of recent work on the modelling and specification of open systems using games and alternating-time temporal logics. In particular, the paper focuses on fundamental semantic questions for those specification formalisms, such as the kind of properties that can be stated in various types of logics for games, and on the computational complexity of their model-checking problems. Enjoy it!

    Friday, January 08, 2010

    My New Workplace

    The School of Computer Science has moved into its premises in the new building of Reykjavik University. The building is still a construction site, and will remain so for a few more months at least. You can see some photos here. There is no doubt that the building looks good. However, I am not so sure that it will offer the best working conditions for academic work. For instance, as a consequence of the downsizing of the building because of the economic crisis in Iceland, we have no offices and we are all sitting in an open space. (I'll try to post a photo of the TCS area when I get a chance to take one.)

    I am not passing judgement yet on the effect that this will have on my work. The next few weeks will allow me to form an opinion on this issue. I will try to keep an open mind and to make the most of what I have available. However, it is hard to escape the nagging thought that I had a quieter working environment when I was a Ph.D. student.

    Stay tuned for more information.