Child care at STOC 2018

Ilias Diakonikolas and David Kempe (STOC 2018 Local Arrangements Chairs) have asked me to post the following announcement, which will be of interest to potential STOC 2018 participants. Kudos to the STOC 2018 local arrangement chairs for organizing the first STOC providing subsidized, pooled childcare.

We are pleased to announce that we will provide pooled, subsidized child care at STOC 2018. The cost will be $40 per day per child for regular conference attendees, and $20 per day per child for students. For more detailed information, including how to register for STOC 2018 childcare, see

http://acm-stoc.org/stoc2018/childcare.html

Ilias Diakonikolas and David Kempe (local arrangements chairs)

ERC Advanced Grants to TCS Researchers

The ERC has announced the latest batch of ERC Advanced Grant recipients. The list of TCS and cryptography researchers who have been honoured with this prestigious accolade includes Peter Bürgisser (hat tip to Artur Czumaj), Jean-Sebastien Coron, Joan Daemen, Herbert Edelsbrunner, Javier Esparza, Joost-Pieter Katoen, Stefano Leonardi and Peter Sewell. Congratulations to all of the grant recipients!

Feel free to suggest additions to the list in the comments section.

Eight four-year PhD positions in Computer Science at the Gran Sasso Science Institute

The Gran Sasso Science Institute (GSSI), based in l’Aquila, Italy, has just issued a call for eight four-year PhD positions in Computer Science. The yearly amount of the scholarship is of € 16,159.91 gross. (An additional 50% on monthly basis may be awarded for research period abroad if approved by the GSSI.) In addition, the following facilities and benefits apply:

• all PhD students will have free accommodation at the GSSI guest house and, starting from the second year, another accommodation or a financial substitute of 350,00 Euros gross/month (to obtain the contribution, the students would have to present a rental agreement in L’Aquila);

• all PhD students will have free luncheon vouchers (1 per day, working days, except school closures, missions, other situations contemplated by the GSSI rules);

• all PhD students will have tuition fees waived;

• all PhD students will be covered by insurance against any accident and/or injury that may occur while carrying out their PhD activities.

For further details see the call for applications at

http://www.gssi.infn.it/phd/docs/2018/CallPhDXXXIV.pdf.

The deadline for applications is the 20th of June, 2018, at 6 pm (Italian time zone).

Ful professorship at Aalborg University

I have been asked to advertise this full professor position at Aalborg University.  For what it may worth, I strongly recommend CS@Aalborg as I working place. 

FULL PROFESSORSHIP AT AALBORG UNIVERSITY
At the Technical Faculty of IT and Design, Department of Computer Science, a permanent Full Professorship in Computer Science is open for appointment starting August 1, 2018 or soon thereafter. The position is enabled by a generous grant from the Poul Due Jensen Foundation and supports the focus areas “Internet of Things and Cyber-Physical Systems” and “Big Data and Artificial Intelligence”.

APPLICATION DEADLINE
Mon Apr 02 00:00:00 CEST 2018

JOB DESCRIPTION
The objective of the position is to strengthen the department’s activities on combining theory and applications in the area of distributed, embedded, and intelligent systems.  Here, current research and teaching span topics such as semantic theories; algorithms and tools for verification and validation; model-driven development, analysis and optimization; and probabilistic models and algorithms for decision making and machine learning.

The position includes funding to recruit an assistant researcher within the research field of the professorship. The assistant researcher position is for four man-years and is funded by the Poul Due Jensen Foundation.

The formal announcement including information about qualification requirements may be found at http://www.stillinger.aau.dk/vis-stilling/?vacancy=953383

You may obtain further professional information from Professor Kim Guldstrand Larsen, phone +45 2217 1159, email: kgl@cs.aau.dk. 

Cs at aalborg university
The Department of Computer Science at Aalborg University is ranked #1 in Denmark according to the Leiden Ranking.

The research at the department features a broad range of synergistic activities within research and education in the general area of computer science, including curiosity-driven research and targeted research in collaboration with industrial partners, as well as traditional university education, with a unique problem- and project-based focus, and continued education and knowledge dissemination. For more information see www.cs.aau.dk.

Noam Nisan receives the EATCS Award 2018

I just saw that the EATCS Awards Committee consisting of Artur Czumaj, Christos Papadimitriou and Jean-Eric Pin (chair) has selected  Noam Nisan as the recipient of the EATCS Award 2018 "for his decisive influence on a range of areas in computational complexity theory and for algorithmic mechanism design, an elegant and rigorous computational theory that aptly informs economics."

The laudatio for the award, which will be presented to Noam at ICALP 2018 in Prague, is available here. Congratulations to Noam!

Most Influential POPL Paper Award 2018: "Multiparty asynchronous session types" by Kohei Honda, Nobuko Yoshida and Marco Carbone

I heard the great news that the paper Multiparty asynchronous session types by the late Kohei Honda, Nobuko Yoshida and Marco Carbone has received the Most Influential POPL Paper Award 2018. See

http://www.sigplan.org/Awards/POPL/.

This award is given annually to the author(s) of a paper presented at the Symposium on Principles of Programming Languages (POPL) held 10 years prior to the award year. The papers are judged by their influence over the past decade.

The citation for the award is available from the above-mentioned web page, but I repeat it here for ease of reference:

Session types are a type-based framework for codifying communication structures and verifying protocols in concurrent, message-passing programs. Previously, session types could only model binary (two-party) protocols. This paper generalizes the theory to the multiparty case with asynchronous communications, preventing deadlock and communication errors in more sophisticated communication protocols involving any number (two or more) of participants. The central idea was to introduce global types, which describe multiparty conversations from a global perspective and provide a means to check protocol compliance. This work has inspired numerous authors to build on its pioneering foundations in the session types community and has initiated many applications of multiparty session types in programming languages and tools. It has also influenced other areas of research, such as software contracts, runtime verification and hardware specifications.

Congratulations to the authors of the paper and to the concurrency community at large, whose work over the last ten years contributed to this award and, most importantly, to significant scientific advances that are now embodied in programming languages and tools that are already having practical impact (see the work with Cognizant, Red Hat, and VMWare on Scribble, and with the OOI), and that I believe will find increasing application in years to come. 

Five Postdoctoral positions in Computer Science at Gran Sasso Science Institute

Five Postdoctoral positions in Computer Science at
Gran Sasso Science Institute in L'Aquila (Italy)
http://www.gssi.it/
Deadline:  2 March 2018 at 6 p.m. (Italian time zone)

The Gran Sasso Science Institute (GSSI, http://www.gssi.it/), a recently established international PhD school and a centre for advanced studies in computer science, mathematics, physics and social sciences offers 18 postdoctoral research positions, five of which are dedicated to computer science and more specifically to themes that are strongly connected to the pillars of the PhD program in computer science:

- Algorithmic foundations of social and computer networks.
- Software systems and services.
- Specifications and analysis of concurrent reactive systems

The research grants are awarded for two years and their yearly amount is € 36.000,00 gross.

Candidates who are preparing their doctoral thesis are eligible to apply; however, they must have obtained their PhD degree before taking up their appointment with GSSI. Selected candidates are expected to start their appointments no later than 1 November 2018.

The application must be submitted through the online form available at www.gssi.it/postdoc/ by 2 March 2018 at 6 p.m. (Italian time zone).

Each application should include the following material:

- the CV of the applicant,

- a research statement,

- up to 3 publications and

- the name and email of two references.

For more information, please consult the Call for Applications at www.gssi.it/postdoc/ or write an email to info@gssi.it.

Prospective candidates are also welcome to contact Luca Aceto (luca.aceto AT gssi.it) or Michele Flammini (michele.flammini AT gssi.it). 

PhD positions at the School of Computer Science, Reykjavik University

The School of Computer Science at Reykjavik University is advertising PhD scholarships. See https://en.ru.is/scs/ph.d-studies/ for details.

The Icelandic Centre of Excellence in Theoretical Computer Science is one of the research centres within the school and is seeking PhD candidates in the following fields: logic and concurrency (contacts: Anna Ingolfsdottir and Luca Aceto), algorithms and distributed computing (contacts: Eyjólfur Ingi Ásgeirsson and Magnús Már Halldórsson), combinatorics and automated proofs (contact: Henning Ulfarsson), types and programming-language semantics (contact: Tarmo Uustalu).

Call for nominations for the 2018 Alonzo Church Award

Catuscia Palamidessi asked me to post the call for nominations for this year's Alonzo Church Award for Outstanding Contributions to Logic and Computation. I encourage all members of the community to nominate their favourite paper or small group of papers in logic and computation published within the past 25 years.


The 2018 Alonzo Church Award for Outstanding Contributions to Logic and Computation
Call for Nominations
Introduction
An annual award, called the Alonzo Church Award for Outstanding Contributions to Logic and Computation, was established in 2015 by the ACM Special Interest Group for Logic and Computation (SIGLOG), the European Association for Theoretical Computer Science (EATCS), the European Association for Computer Science Logic (EACSL), and the Kurt Gödel Society (KGS). The award is for an outstanding contribution represented by a paper or by a small group of papers published within the past 25 years. This time span allows the lasting impact and depth of the contribution to have been established. The award can be given to an individual, or to a group of individuals who have collaborated on the research. For the rules governing this award, see: http://siglog.org/awards/alonzo-church-award/.
The 2017 Alonzo Church Award was given jointly to Samson Abramsky, Radha Jagadeesan, Pasquale Malacaria, Martin Hyland, Luke Ong, and Hanno Nickau for providing a fully-abstract semantics for higher-order computation through the introduction of game models, see: http://siglog.org/winners-of-the-2017-alonzo-church-award/.
Eligibility and Nominations
The contribution must have appeared in a paper or papers published within the past 25 years. Thus, for the 2018 award, the cut-off date is January 1, 1993. When a paper has appeared in a conference and then in a journal, the date of the journal publication will determine the cut-off date. In addition, the contribution must not yet have received recognition via a major award, such as the Turing Award, the Kanellakis Award, or the Gödel Prize. (The nominee(s) may have received such awards for other contributions.) While the contribution can consist of conference or journal papers, journal papers will be given a preference.
Nominations for the 2018 award are now being solicited. The nominating letter must summarise the contribution and make the case that it is fundamental and outstanding. The nominating letter can have multiple co-signers. Self-nominations are excluded. Nominations must include: a proposed citation (up to 25 words); a succinct (100-250 words) description of the contribution; and a detailed statement (not exceeding four pages) to justify the nomination. Nominations may also be accompanied by supporting letters and other evidence of worthiness.
Nominations should be submitted to catuscia@lix.polytechnique.fr by March 1, 2018. 
Presentation of the Award
The 2018 award will be presented at ICALP 2018, the International Colloquium on Automata, Languages and Programming. The award will be accompanied by an invited lecture by the award winner, or by one of the award winners. The awardee(s) will receive a certificate and a cash prize of USD 2,000. If there are multiple awardees, this amount will be shared.
Award Committee
The 2018 Alonzo Church Award Committee consists of the following five members: Thomas Eiter, Javier Esparza, Catuscia Palamidessi (chair), Gordon Plotkin, and Natarajan Shankar.

First-year computer science students at the GSSI publish paper at ICSE 2018

The paper "FAST Approaches to Scalable Similarity-based Test Case Prioritization" by Breno Miranda (UFPE, Brazil), Emilio Cruciani (GSSI, Italy), Roberto Verdecchia (GSSI, Italy, and Vrije Universiteit Amsterdam, NL) and Antonia Bertolino (ISTI - CNR, Italy) has been accepted as a technical research paper at ICSE 2018, the 40th International Conference on Software Engineering. ICSE is the flagship conference in Software Engineering and is very selective its technical-research-paper track is the most prestigious one within the conference.

The paper contributes to the classic area of software testing, which is one of the approaches developed by computer scientists to increase their confidence that computing systems actually do what they were designed to achieve. Since the number of tests that can be performed on a computing system is enormous, test-case prioritization is a crucial element in any practical testing framework. In that approach, one prioritizes test cases so that they can detect faults more efficiently using the available limited resources.

The paper to be presented at ICSE 2018 is the first that applies techniques from data mining to test case prioritization. In particular, it shows that the use of ideas from locality-sensitive hashing, a technique stemming from research in TCS that has been employed to great effect in approximate similarity searches in audio and video data, amongst others, leads to effective test prioritization in practice, when one needs to select tests effectively amongst millions of possible ones.

Antonia Bertolino is a member of the Scientific Board for the PhD programme in Computer Science at the GSSI. Breno Miranda is currently a postdoctoral researcher in Brazil and is one of Antonia Bertolino's former PhD students. Emilio Cruciani and Roberto Verdecchia just started their second year as PhD students in computer science at the GSSI and the paper to be presented at ICSE 2018 builds on their project for the first-year Software Testing course held in early 2017 at the GSSI by Antonia Bertolino. The project itself arose from a question asked by the students during the lectures. This is what inspiring, research-based teaching can produce when there is intellectual chemistry between lecturers and students.

Congratulations to the authors (and to the computer science group at the GSSI)!

Tenure-track positions in CS at Reykjavik University

We are aggressively recruiting new tenure-track faculty in Computer Science to Reykjavík University (https://en.ru.is/scs/). Theoretical computer science is one of the focus areas mentioned in the call. This is a link to further information:

http://radningar.hr.is/storf/ViewJobOnWeb.aspx?jobid=3111

Whereas Reykjavík University is relatively small, I believe we can offer junior faculty attractive opportunities and an independent career path. Reykjavík is a great place for families to live, has a vibrant cultural scene and is attractive to people who enjoy the outdoors.

I would very much appreciate your help in getting this job announcement seen by interested potential candidates.

A letter to Franklin Foer (guest post by Frits Vaandrager)

Frits Vaandrager has sent the appended letter, which I am posting with his kind permission, to the journalist Franklin Foer. (The letter is also available here.)

Frits wrote to me saying that:

Franklin Foer published an interesting book, World without Mind, that was named a "Notable book of 2017" by the New York Times. According to Foer,  computer scientist started to use the term "algorithm" because of "status anxiety", as a form of name dropping by programmers to suggest that they were also serious scientists. In my letter to Foer I give some historic evidence that this framing is utterly incorrect, but I'd be interested in the views of colleagues from the TCS community on this matter.

Please share your views on this matter as comments to this post. It is important to put the record straight and I am glad that Frits took the time to write a cogent letter to Mr. Foer. Thank you!

Dear Mr Foer,

With much interest I have read your book “World without mind”. I agree with many of your conclusions! But as a computer scientist who has been working on algorithms for more than 30 years, I am also deeply troubled by one paragraph in your book: 

“For the first decades of computing, the term “algorithm” wasn’t much mentioned. But as computer science departments began sprouting across campuses in the 60s, the term acquired a new cachet. Its vogue was the product of status anxiety. Programmers, especially in the academy, were anxious to show that they weren’t mere technicians. They began to describe their work as algorithmic, in part because it tied them to one of the greatest of all mathematicians – the Persian polymath Muhammad ibn Musa al-Khwarizmi, or as he was known in Latin, Algoritmi. During the 12th century, translations of al-Khwarizmi introduced Arabic numerals to the west; his treatises pioneered algebra and trigonometry. By describing the algorithm as the fundamental element of programming, the computer scientists were attaching themselves to a grand history. It was a savvy piece of name-dropping: See, we’re not arriviste, we’re working with abstractions and theories, just like the mathematicians!”

 

Do you have historic sources for these strong statements? 

Much of computer science is rooted in the work of mathematicians and logicians such as Turing, Church and von Neumann. These researchers used the word “algorithm” already before computers were built, see for instance p349 of Alonzo Church’s 1936 paper “An unsolvable problem of elementary number theory”. Together with Turing’s 1936 paper “On computable numbers, with an application to the entscheidungsproblem”, this paper forms the basis for the so-called Church-Turing thesis, which in turn laid the foundation of theoretical computer science. The computer science pioneers definitely knew the term “algorithm”!!

The term “algorithm” was maybe not used so often by computer scientists during the initial years (often they used terms such as “effective procedure” or “computable function”), but that certainly changed in 1958 with the influential work on ALGOL (short for Algorithmic Language), a family of imperative computer programming languages. The researchers who worked on Algol e.g. Bauer, Backus, Dijkstra, Perlis, Naur, van Wijngaarden & McCarthy were established scientists who definitely did not suffer from “status anxiety”. Backus, Dijkstra, Perlis, Naur and McCarthy later received the Turing award, the major prize for computer science research, for their groundbreaking research.

In order to appreciate the wonderful scientific work on algorithms, I can recommend you, for instance, to read the book Algorithmics – The spirit of computing by David Harel. I hope that, after studying this book, you will be also convinced that the fact that programmers used the term algorithm is not a form of name dropping. The work on algorithms since the advent of computers very much fits into the tradition of the work started by great scientists like Euclides and al-Khwarizmi.

Scientific knowledge may always be used for both good and bad things. Like you, I am very concerned about the use of algorithms by Google, Facebook, Apple and Amazon. But I disagree with any suggestion that there is no science behind computer science algorithms!

Looking forward to your reaction, with best regards,

Frits Vaandrager

Professor of Computer Science at Radboud University

Nijmegen, December 4, 2017

Two and a half months at the Gran Sasso Science Institute

About two and a half months have passed since I started working at the Gran Sasso Science Institute (GSSI). I still have much to learn about the functioning of the Italian university system (and even of the GSSI), and it is already clear that there will be many of its aspects that I will probably never learn. However, my impression so far is that the level of bureaucracy in Italy is definitely higher than that in the countries where I have previously worked.

On page 88 of this interesting article, the historian Rogers Hollingsworth writes:

"One of the factors influencing creativity at the level of the nation state is the institutional environment in which scientists conduct research. I code scientific institutional environments as ranging from weak to strong. Weak institutional environments exert only modest influence (1) on the appointment of scientific personnel of research organizations, (2) in determining whether a particular scientific discipline will exist in a research organization, (3) over the level of funding for research organizations, (4) in prescribing the level of training necessary for a scientific appointment (e.g., the habilitation), and (5) over scientific entrepreneurship (e.g., the norms of individualism that socialize young people to undertake high-risk research projects). Strong institutional environments are at the opposite end of the continuum on each of these characteristics. Weak institutional environments have tended to facilitate greater scientific creativity in a society than strong institutional environments..."

(The emphasis is mine.) According to the above description, the Italian scientific institutional environment can only be classified as strong, for good or for worse. Fortunately, the GSSI is a centre for advanced studies and an international PhD school. Even though it has to follow the Italian law, with all its quirks, it is more nimble and less rigid  than the average Italian university. Moreover, most of the bureaucracy is hidden to the junior members of our faculty, such as the assistant professors, who can largely concentrate on the scientific work.
 
I have always appreciated the work that Italian researchers have been carrying out over the years, but what I have seen so far has increased my esteem for them even more. In spite of the extremely rigid system within which they are forced to operate, they manage to be productive and to maintain a strong commitment to their research work, achieving a high level of scientific production, both in quality and in quantity. The GSSI hosts a number of top-class academics in its four fields of research (computer science, mathematics, physics and social sciences) and this creates a stimulating environment for faculty and students alike.

The computer science group at the GSSI is still too small, but it seems to me that it punches well above its weight. Its members are very dedicated and have done an amazing job since the beginning of the GSSI adventure. (It was a humbling learning experience for me to present their achievements to the Scientific Advisory Board of the GSSI last Monday.)

It is clear that our group needs to grow, but we want to do so well. If you work in one of the research areas that we cover, at their intersection or in sister ones, and you think you'd be interested in working in L'Aquila with our faculty, do drop one of us a line, sending your CV and an expression of interest. We are keen to recruit strong researchers at all levels who can help us build the best international research centre in computer science we can. I can vouch that the computer science group at the GSSI provides young researchers with early-career autonomy in a nurturing environment, which isn't very common in Italy (as far as I know), and with the opportunity to become involved in the supervision of doctoral students. There are also resources for inviting collaborators and organizing thematic events, amongst other things.

It will be interesting to see how the computer science group will develop at the GSSI over the coming year. 

Reykjavik University: A THE top-500 university

Reykjavik University is in the top 500 universities in the world, according to the THE rankings. See here for details about my Icelandic workplace.

This is the first time RU appears on the list, which is an excellent result for a young and specialized university.

Even though all rankings should be taken with a pinch of salt, this is a remarkable achievement for a small university in a tiny country. Congratulations to my colleagues at Reykjavik University, who made this achievement possible with their work in research, teaching and service to the academic community.

Computer Science at the Gran Sasso Science Institute

I recently advertised a call for four PhD positions in computer science at the Gran Sasso Science Institute (GSSI) in L'Aquila, Italy. That post included a link to a web site with some information about the GSSI. However, some potential applicants, and colleagues in general, might be interested in knowing more about the CS group in this new institute, without having to browse through a series of web pages. I therefore decided to collect some relevant information on CS@GSSI in this blog post in the form of a FAQ, hoping it may be of help to students and computer science researchers who might wish to consider working at the GSSI.

1. What is the GSSI? The GSSI is a recently established university in Italy. It is an institute for advanced study and an international PhD school, having English as its official language. It is located in L'Aquila, Italy, in the beautiful Abruzzo region. It focuses on astroparticle physics, computer science, mathematics and urban studies.
2. What areas of CS are covered at the GSSI? Information on research at CS@GSSI may be found here. In short, CS@GSSI is based on three main areas, namely the algorithmic study of computer and social networks (as covered, for instance, by ICALP Track A and Track C), specification and analysis of reactive systems, and software engineering techniques for building usable and easily maintainable distributed applications. 
3. Who works at CS@GSSI? CS@GSSI is still in its infancy and has ambitious growth plans in the short to medium term. In the area of algorithms, Michele Flammini, Gianlorenzo D’Angelo (recipient of the “Best Italian Young Researcher in Theoretical Computer Science” award for 2016 of the Italian Chapter of the European Association for Theoretical Computer Science) and Mattia D’Emidio have been the first researchers working at GSSI. Rocco De Nicola (whose main affiliation is at IMT Lucca) has been the director of the CS programme and has spearheaded the work in formal methods, together with Omar Inverso. I joined the GSSI as a professor today. Work in software engineering has been carried out by Ludovico Iovino, Catia Trubiani and people in the high-profile research group in SE at the University of L'Aquila led by Paola Inverardi. Former GSSI postdoc Ivano Malavolta is now an assistant professor in Data-Driven SE at VU Amsterdam, and is jointly supervising some students at GSSI.
4. Apart from the faculty at GSSI, with whom can PhD students interact at CS@GSSI? CS@GSSI has a vibrant guest lecturer programme, with frequent visits by top-class researchers from all over the world, as well as affiliated faculty. See here for the details. (Look for "Scientific collaborators" and "Lecturers from other institutions".)
5. How is the scientific environment at CS@GSSI? The group runs a seminar series and has already hosted conferences and workshops. See here for some information. It will soon organize SAGT 2017 at GSSI. Other events are in the works.
6. How many PhD students in CS are there? What do the graduates do after their PhD? CS@GSSI hosts about 30 PhD students at all times. You can see the list of current students here. The institute is only about three years old, so only some of the first batch of students have graduated or are about to do so. Of those, all of them have found postdoctoral positions at institutions in Italy. Two GSSI students who just submitted their theses will join Jukka Suomela's group at Aalto University from January 2018.

If you have any further questions, please post a comment to this post, so that I can keep the FAQ up to date and as informative as possible.

Call for GSSI PhD Applications in Computer Science now open

Encourage students interested in TCS (both volume A and volume B) and Software Engineering to apply for these four PhD positions in Computer Science at the Gran Sasso Science Institute! The deadline is the 18th of September.

The Gran Sasso Science Institute (GSSI) offers 4 PhD positions in Computer Science for the academic year 2017/18.

The fellowships are awarded for three years and their yearly amount is € 16,159.91 gross. All PhD students have free accommodation at the GSSI facilities and use of the canteen.

The application must be submitted through the online form available at www.gssi.it/phd/ by September 18, 2017 at 18.00 (Italian time zone).

For more information, please consult the Call for Applications at www.gssi.it/phd/ or write an email to info@gssi.it or call +39 0862 4280262.

Proofs of the Dichotomy Conjecture (guest post by Petar Marković)

I have received the following contribution by Petar Marković, who summarizes recent developments related to the three proofs of the Dichotomy Conjecture that have been proposed since the start of the year and provides an overview of the proofs by Bulatov and Zhuk. The first part of the post is based on a comment Petar posted here. The second is more technical and provides an overview of the proofs by Bulatov and Zhuk, which will be presented at FOCS 2017. I hope that Petar's overview will entice some experts who have not read those proofs to do so and will help them  as they delve into the technicalities. Thanks to Petar for taking the time to summarize his understanding of the proofs with the community. 

Addendum dated 12 December 2017: Bulatov and Zhuk have shated the best paper awards at FOCS 2017 with Ola Svensson and Jakub Tarnawski. See here. Thanks to Lance Fortnow for sharing this piece of news with me.

Status of the three proposed proofs for the Dichotomy Conjecture

As several people in the community have been aware of, the proof of Feder, Kinne and Rafiey has been suspect since it appeared. The parts where they are unclear, or wave hands over details, are precisely the parts where, in the opinion of several experts, the main difficulty was. Unfortunately, this has led to a counterexample and the retraction by Feder, Kinne and Rafiey of the claim they have solved the Dichotomy Conjecture. Their retraction can be found in the comments which replace the abstract of the fourth and most current version of their paper, see https://arxiv.org/abs/1701.02409.

More concretely, it was pointed out in private conversation of several experts that their proof fails on Miklós Maróti's ‘tree-on-Mal’cev’ kind of problems, when they are eliminating what they call `non-minority cases'.

Incidentally, ‘tree-on-Mal’cev’ is not some obscure class of CSPs. As people who are reading it will surely agree, generalizing Maroti's result to 'semilattice-on-Mal’cev’ is the cornerstone of Andrei Bulatov's proof of the Dichotomy Conjecture, the rest is a (very technical and difficult) generalization of the ideas which solve this special case. Even though Feder, Kinne and Rafiey were working only on digraph templates, while ‘tree-on-Mal’cev’ does not specify the relations, just the polymorphisms, the construction by Bulin, Delić, Jackson and Niven, which improves on the original one by Feder and Vardi, reduces a general template to a digraph one, while preserving not only the complexity but also most polymorphisms. So Feder, Kinne and Rafiey's algorithm should have been able to solve those ‘tree-on-Mal’cev’ templates.

Ross Willard, who also was among the experts involved in the initial conversation in January, took the trouble to actually construct digraph CSPs out of the 'tree-on-Mal'cev' CSPs. He constructed out of a tree-on-Mal’cev template a digraph template which contradicts the claim in Feder, Kinne and Rafiey paper that certain situation in the digraphs allows the domain of a variable, and thus the multi-sorted instance, to be reduced by a vertex. This contradicts the whole philosophy of their approach, creating a barrier where they can't proceed with reductions. He emailed the authors of Feder/Kinne/Rafiey his counterexample and, working together, they simultaneously published the retraction, while he published his counterexample on arxiv. The counterexample is available at https://arxiv.org/abs/1707.09440.

On the flip side, at a fairly large conference in June in Novi Sad, Serbia, both Bulatov and Dmitriy Zhuk had plenary talks. After the afternoon in which they exposed their proofs of the Dichotomy Conjecture to a general audience, a special event was organized which lasted almost three hours. The idea was that each would discuss minutiae of their proofs and answer challenges from present experts. In the audience there were about a dozen people who may safely be called experts on the algebraic approach to CSP and most have read in detail large parts of both proofs. There were many interruptions and serious questions were asked, but both proofs survived all challenges unscathed. My degree of confidence after this event in both Bulatov's and Zhuk's proofs is very high, well over 90%, and the odds that both are wrong are really small.

Overview of the proofs by Bulatov and Zhuk

The proof by Bulatov has several ingredients: 

1. his own colored graph theory of algebras which he has been developing for the past decade or so and which he additionally improved on for this paper,

2.  a new centralizer notion which is similar to the classical one from 1980’s Freese and McKenzie book, but this one involves binary polynomials instead of terms of arbitrary arity,

3. a connectedness notion, dubbed ‘coherent sets’, between domains of various variables, somewhat reminiscent of what McKenzie and I called ‘strands’ in an unpublished paper about semilattice-over-Mal’cev CSPs, but much more complicated

4. Maróti’s reduction which solves one of his reduced cases. This reduction uses polynomials of the polymorphism algebra (operations created from polymorphisms by fixing some variables as constants) to find a related smaller CSP instance, which either has no solution, in which case the original one doesn’t have a solution, or has a solution, in which case that solution shows how to reduce the original instance to a smaller one,

5. a crazy amount of consistency which assures that another of his three reduced cases must have a solution if it is nonempty,

6. the old few subpowers algorithm in his third reduced case, and finally

7. a massive induction which lowers the location of congruence covers modulo which coherent sets are considered, working simultaneously through various congruence lattices of variable domains. When they can appear only at the bottom then the reduced cases 4., 5. and 6. occur. It is this last part which is the hardest and requires most scrutiny. The rest is mostly clear to experts (personally, I would say I am sure the rest is correct).

I understand Zhuk’s proof much less, but the main ingredient is his structure theory of relations. He subjects the constraint relations to several extreme conditions he invented (and can assume after some effort). Next, he also works down the congruence lattices of various domains of variables. There are three types of reductions he uses to reduce to an instance which satisfies all these assumptions. When the congruences have also been subjected to extreme assumptions, then his theory of relations claims that each lower cover of the current congruence in each domain of variable is a Mal’cev cover. He can solve the Mal’cev problem, which is pretty much a system of linear equations, and arrive at the solution space to the factor problem. Also, he can test whether this is the same space as the space of all solutions to the initial instance, factored. This is easy, he just selects one solution of the factored problem and uses its classes as new domains of variables. They are smaller than the original ones so inductively he can solve it. If it has a solution, he found a solution to the original instance. If not, he works on finding a new constraint which does not affect the solution space to the original instance, but reduces the dimension of the solution space to the factor problem. (Finding this constraint relies on his structure theory and on other reductions, and is probably the hardest part of his proof.)

There is a circular nature to Zhuk’s proof which uses all four types of reductions in previous cases to prove the one he is currently applying. This is an idea similar to ‘simultaneous induction’ in Adian and Novikov’s proof of Burnside conjecture which was later much used in group theory.

The very high-level bird-eye view is that Bulatov reduces everything to consistency checking or few subpowers (when there are no ‘semilattice edges’), Zhuk reduces in a circular way, but Mal’cev is what he seems to end at, while Feder, Kinne and Rafiey also reduce everything to Mal’cev, but have a problem in eliminating some semilattice covers. Since the absence of semilattice covers is the same as having few subpowers, the missing part in Feder, Kinne and Rafiey is serious.

Why you should join the EATCS and convince your colleagues to do so too

Let me state at the outset that, as former president of the EATCS, I am somewhat biased on the matter I cover in this post. However, I do believe that what I write below is based on facts rather than bias. I hope that you will draw your own conclusions and join a scientific associations that provides sterling support for theoretical computer science as a whole.

The first question I am typically asked when I encourage a colleague to join the EATCS is  "What is in it for me?" This question is natural and easy to answer (see here), but I believe that it is the wrong question to ask. As someone who has lived a fair number of years in sunny, socialist Scandinavia and a closely related country, I have grown into thinking that a better question would be "What's in it for the TCS community?" To my mind, the answer to this second question is even clearer.

The EATCS is a scientific association that, compatibly with its limited resources, does much for TCS.

• Its Bulletin has been open access for over ten years. Anyone can read it for free, unlike many other bulletins and newsletters that are only available to members of professional societies. This is made possible by the support of the EATCS members for the benefit of everyone. 
• The proceedings of ICALP have been open access since last year. The association lost money by deciding to go for open-access proceedings, but its council felt that the time had come to serve the community in this way. 
• The EATCS provides financial support to conferences and young researcher schools, and sponsors prizes and awards that put TCS research in the limelight. When I was the president of the EATCS, I was surprised to receive sponsorship requests from the organizers of conferences that were officially "sponsored" by incomparably larger and richer professional societies. The EATCS provided a small financial sponsorship to some of those events, as part of its mission. Now I have a better idea of why those conferences were asking for EATCS sponsorship. 
• Conferences that collect EATCS membership fees receive some of those fees back from the association. I have come to understand that this is not the case for other professional societies. 

I could go on, but this short list should be sufficient to help you make up your mind and I do not want this post to turn into a rant. The bottom line is that by joining the EATCS, you will support TCS for a mere 30 € per year (two years if you are a student). Do you need more reasons to join and help the community?

If you have any questions or doubts, air them as comments to this blog post. 

Call for guest bloggers at ICALP 2017

I would like to have some blog coverage for ICALP 2017. If you are attending the conference in Warsaw and you are interested in guest blogging, drop me a line. Ideally, I would like to have a guest blogger for each of the tracks in the conference. You are, of course, also most welcome to blog about the invited talks, the award ceremony, the general assembly, the affiliated workshops and any other aspect of the conference you fancy. 

Unfortunately, I cannot attend ICALP this year, so there won't be any reporting from me. 

 

Tenure-track assistant professorship (cyber security) at IMT Lucca

I have been asked to distribute this job announcement. For what it is worth, I strongly recommend IMT Lucca, an ambitious doctoral school and centre of advanced studies, and Lucca is a wonderful place to live.

IMT School for Advanced Studies Lucca invites applications for a tenure-track assistant professorship in Computer Science
(Ricercatore a Tempo Determinato Tipo B, RTD-B - INF/01).

We particularly welcome candidates with experience or willingness to work in the area of cyber security broadly construed, ideally complementing IMT’s current strengths. Topics of interest include (but are not limited to):
- access control;
- cryptocurrencies;
- formal verification of security protocols;
- security requirements elicitation;
- web security;
- security of “Internet of Things”.

The successful candidate is expected to publish in first-class journals and in the proceedings of top conferences in computer security. Moreover, she/he is expected to establish links with local companies and institutions that have shown high interest in cybersecurity, and to apply for national and international research funding.

According to Italian law, RTD-B assistant professors will be employed for three years, during which they are required to secure a habilitation (ASN) from an independent national evaluation committee in order to obtain tenure at the associate professor level. Applicants to ASN are evaluated based on various indicators of scientific quality and leadership such as bibliometrics, research grants, invited talks, and best-paper awards.

IMT is one of Italy’s six schools of excellence for postgraduate education, ranked first in the last national research assessment exercise. IMT researchers are expected to contribute to the teaching and supervision of PhD students, admitted to the School through a selective international competition. The working language is English.

The salary will be determined on a personal basis within pay grades defined as per Italian legislation. The indicative starting gross salary for an RTD-B assistant professor is € 34,898. Net income may vary depending on income taxes, local taxes, retirement plan, health care deduction and tax exemptions. New employees who have worked in research-based positions abroad for the previous two years may be eligible for a substantial tax rebate for the first three fiscal years of employment.

The online application form is available at
https://www.imtlucca.it/school/job-opportunities/academic/341
!!!!!Deadline July 27th, 2017 - Italian midday!!!!!