Logic Activities in Europ e y Yuri Gurevich 1 Intro duction During Fall 1992, thanks to ONR, I had an opp ortunity to visit a fair number of West Eu- rop ean centers of logic research. I tried to learn more ab out logic investigations and appli- cations in Europ e with the hop e that my exp erience may b e useful to American researchers. This rep ort is concerned only with logic activities related to computer science, and Europ e here means usually Western Europ e (one can learn only so much in one semester). The idea of such a visit may seem ridiculous to some. The mo dern world is quickly growing into a global village. There is plenty of communication b etween Europ e and the US. Many Europ ean researchers visit the US, and many American researchers visit Europ e. Neither Americans nor Europ eans make secret of their logic research. Quite the opp osite is true. They advertise their research. From ESPRIT rep orts, the Bulletin of Europ ean Asso ciation for Theoretical Computer Science, the Newsletter of Europ ean Asso ciation for Computer Science Logics, publications of Europ ean Foundation for Logic, Language and Information, publications of particular Europ ean universities, etc., one can get a go o d idea of what is going on in Europ e and who is doing what. Some Europ ean colleagues asked me jokingly if I was on a reconnaissance mission. Well, sometimes a cowwants to suckle more than the calf wants to suck (a Hebrew proverb). It is amazing, however, how di erent computer science is, esp ecially theoretical com- puter science, in Europ e and the US. American theoretical computer science centers heavily around complexity theory. The two prime American theoretical conferences | ACM Sym- p osium on Theory of Computing (STOC) and IEEE Foundation of Computer Science Con- ference (FOCS) | are largely devoted to complexity theory (in a wider sense of the term). That do es not exclude logic. As a matter of fact, imp ortant logic results have b een published in those conferences. However, STOC and FOCS logic pap ers b elong, as a rule, to branches of logic intimately related to complexity. Finite mo del theory is a go o d example of that; see [Fagin 1990, Gurevich 1988] and esp ecially [Immerman 1989]. The di erence b etween theoretical computer science and the rest of computer science (and computer engineering) is relatively well delineated in this country. In Europ e, the line b etween theoretical computer science and the rest of computer science and engineering is much more blurred, partially b ecause computer science and en- gineering in general are more theoretical. A much greater prop ortion of Europ ean research go es into programming language theory,semantics, sp eci cation languages, pro of systems, veri cation metho ds, etc. For brevity and the lack of a b etter term, I will use the term \formal metho ds" for all of these areas. Europ eans put much more faith and e orts into ACM SIGACT NEWS 25, No. 2, June 1994, 11{24. y Supp orted by ONR grant N00014-91-J-1861. EECS Dept., UniversityofMichigan, Ann Arb or, MI 48109-2122, [email protected] 1 foundational investigation of software and hardware technology and into developing formal metho ds for use in software and hardware. Of course, things are not black and white. For example, the American conference on Principles of Programming Languages is very theoretical (and Europ ean in uence can b e easily discerned there), and there are excellent complexity theorists in Europ e. Nevertheless the gap is huge and, to a great extent, it is the gap b etween the complexity and formal metho ds communities. The rst is centered heavily in the US; there is a fair number of reputable complexity theorists in Germany, but your ngers may suce to count them in France or Great Britain. The second spreads more evenly but plays a much greater role in Europ e. Only a few p eople work b oth in complexity and formal metho ds. An interesting example of the Europ ean version of the split b etween the twocommunities is the Computer Science DepartmentofEdinburgh University in Scotland. They havetwo disjoint seminars. One is their Theory Seminar. It is huge (as theory seminars go) and devoted to semantics and formal metho ds in general; it is as go o d as any formal-metho ds seminar in the world. The other one is devoted to complexity theory, also of excellent quality, but tiny.(Ispoke in b oth seminars and was told that such incidents are rare indeed.) To o often complexity theorists are not interested at all in semantics and (what we call here) formal metho ds, and to o often exp erts in formal metho ds are not interested in and do not know mo dern complexity theory.Furthermore, the formal metho ds eld itself splits into a numb er of areas sp eaking very di erent languages. Yes, there are numerous visits of Americans to Europ e and Europ eans to the US, but all to o often complexity theorists go to sp eak to complexity theorists and formal metho ds exp erts go to sp eak to formal metho ds exp erts in their area even if they all go to the same conference. One meets American researchers dismissing Europ ean computer science as largely irrelevant, pure logic. And one militantFrench computer scientist told me that complexity theory is irrelevant pure mathematics. He is not typical and the phrase was thrown during a heated discussion, but the sentiment of that phrase is not completely foreign to many in Europ e. I had to decide whether to concentrate on a few carefully chosen areas or to try to cover Europ ean logic activities in general. The latter task seemed frighteningly hard. Logic p ermeates all areas of computer science in Europ e, and Europ ean logic activities are so intensive and diverse that it would take a large committee and longer time to survey them prop erly. On the other hand, particular elds are surveyed from time to time by exp erts who know the researchers and the pap ers and can write surveys without the opp ortunities of sp ecial learning tours, whereas I didn't knowofany general study of Europ ean logic activities. The opp ortunity of a learning tour seemed to suggest the more ambitious general study. After a p erio d of hesitation, I decided to do that, and I sp entmuch of the Europ ean tour learning things I did not know and talking with p eople with whom I had had little or no interaction b efore. In this rep ort, I am not going to catalog who is doing what in Europ e. It makes no sense for one p erson to attempt to compile a comprehensive survey of Europ ean logic activities in few months. As I mentioned earlier, it would take more p eople and more time to write a comprehensive survey. Moreover, such a survey has b een published recently: [van Leewen 1990, volumes A and B]. But, to illustrate howmuch is going on in Europ e, British logic activities are sketched in Section 2. Why British? Well, my division of computer science into Europ ean and American is not strictly geographic. I am trying to discern typical and distinguishing Europ ean tendencies, and Great Britain is very Europ ean in that sense. If you want to knowhow it feels to bring coals to Newcastle, give a formal metho ds talk in UK. That is how I felt in March 1992 at the 8th British Collo quium for Theoretical Computer 2 Science in . Newcastle up on Tyne, England. It is somewhat surprising that theoretical computer science is so di erent in the UK and the US; after all, we share roughly the same language. But theoretical computer science is not the only eld where British hold their own; British TV is another such eld. Another reason for concentrating on UK is that Wilfrid Ho dges volunteered to write that sketchforme.Infact,Ispent more time in France with its own rich logic culture. Section 3 is devoted to p ositive sides of the Europ ean way of doing things; there are things for us to learn. Section 4 is devoted to other comments. The learning tour in Fall 1992 a ected me a great deal even though I had visited Europ e many times b efore and was familiar with Europ ean computer science and many prominent Europ ean computer scientists. The tour and the rep ort have b een hard work, but I enjoyed it. The tour gave me a wider p ersp ective. I was esp ecially impressed by Europ ean b oldness in promoting formal metho ds. That b oldness is contagious. In spite of the criticism that I have for Europ ean ways of doing things, the tour gave me more con dence that a logician may b e of great help to software engineers and even himself/herself may b e a successful software engineer. Acknowledgments. It is a pleasure to thank ONR for the supp ort and for trust- ing my judgment and not micromanaging the tour; to thank INRIA Ro quencourt for the excellent condition for mywork in Paris; to thank my Europ ean colleagues for invitations, explanations and for b eing so generous with their time; to thank Wilfrid Ho dges for the sur- vey of British logic activities; to thank my colleagues Krzysztof Apt, Andreas Blass, Egon Borger, Thierry Co quand, Gordon Plotkon, Dean Rosenzweig, Victor Vianu and Moshe Vardi for comments on earlier versions of the rep ort.