The seminar took place from 20th until 25th June 2010.
Its primary aim was to foster interaction between researchers
working on modelling programs/proofs using games and
the verification community. The meeting brought together 
28 researchers from eight different countries,
both junior and senior, for a systematic assessment of what 
the two areas have to offer to one another,
critical evaluation of what has been achieved so far, 
with a view to establishing common research goals for the future

Mellies, Paul-Andre

Murawski, Andrzej S.

Schalk, Andrea

Walukiewicz, Igor

Dagstuhl Research Online Publication Server

10252 Executive SummaryGame Semantics and Program Veriﬁcation Dagstuhl Seminar Paul-André Melliès1, Andrzej S. Murawski2, Andrea Schalk3 and IgorWalukiewicz41 University VII - Paris, FRmellies@pps.jussieu.fr2 University of Oxford, GBAndrzej.Murawski@comlab.ox.ac.uk3 University of Manchester, GBA.Schalk@cs.man.ac.uk4 LaBRI - Bordeaux, FRigw@labri.frThe seminar took place from 20th until 25th June 2010. Its primary aim wasto bring together researchers working on modelling programs/proofs using gamesand the veriﬁcation community. It was clear to us that both communities could,at this point in time, begin to proﬁt from the methods and insights gained bythe other community, and be able to help with some of the other side's unsolvedproblems. So far the two groups have had very little interaction with each other,although there are some researchers who are active in both areas.We organized the schedules on a day-to-day basis, in order to be as reactive aspossible to the requests and questions coming from the discussions. We were alsocareful to leave a lot of time for interaction, while oﬀering most participants theopportunity to give a talk. Twenty-two talks were delivered during the meeting.1 Scientiﬁc contentThe ﬁeld of program veriﬁcation aims to identify and implement techniques forautomatic certiﬁcation of program correctness or desirable program behaviour.A central task in any software veriﬁcation project is the choice of a modellingapproach and a decidable formalism in which the model will be represented forthe purpose of veriﬁcation.Game semantics uses the metaphor of game playing to interpret computation,which it views as an exchange of moves between two players. This allows fora very concrete account of interaction consisting of sequences of moves, onethat can be readily represented with common formalisms used in veriﬁcation.As it turns out, this opens up the way to numerous applications. On the moreabstract level, game semantics  as a modelling technique  oﬀers a sophisticatedabstraction mechanism, which enables one to describe what is observable in aprogram behaviour rather than what internal symbolic steps the programs make.Our seminar began with two tutorial talks (Ghica, Murawski), which aimedto introduce the basic principles behind game semantics, outline its place in theDagstuhl Seminar Proceedings 10252Game Semantics and Program Veriﬁcationhttp://drops.dagstuhl.de/opus/volltexte/2010/27932 P.-A. Melliès, A. S. Murawski, A. Schalk and I. Walukiewiczlandscape of programming language semantics and convey its ﬂavour. Ghica'stalk was a survey of domains in which game semantics has been applied todate, including static analysis, equivalence checking and hardware synthesis.He also described veriﬁcation tools whose engine is founded on game-semantictechniques, and outlined a variety of techniques employed to guard against stateexplosion in game models. Murawski discussed the anatomy of game models andpresented a simple model that could be described with regular expressions. Themodel has formed the core of several tools implemented so far and is a good pointof entry into the area. The concept of strategy composition was then introducedin detail and its crucial role in constructing game models was elaborated. Finally,the principle of full abstraction was mentioned along with the advantages thatit oﬀers in veriﬁcation tasks.On the ﬁrst day we also had extended talks on topics in which game semanticshas already proved to be an eﬀective tool or seems to be emerging as a potentiallyuseful technique to ensure further progress. Kobayashi discussed model-checkingfunctional programs via higher-order recursive schemes. The ﬁrst decidabilityprocedure for the latter was based on games and broke a long-standing stalematein the ﬁeld several years ago. Since then, alternative approaches were proposed(notably using suitably crafted type systems) and it remains to be seen whatrole game models will play in the future in that area. Kobayashi outlined thedirections in which research on the analysis of functional programs is proceedingand suggested a few problems which game semantics might help to address. Ni-wi«ski later gave a complementary talk about an automata-theoretic approachto analyzing higher-order recursive schemes. Hofmann, in turn, described a prob-lem (side-eﬀect freeness) that he and his collaborators have been attacking usingtechniques based on logical relations. Quite interestingly, it turned out that thesolution they have arrived at can be interpreted in a natural way in the spiritof game semantics, which calls for further investigation. Other unifying talksalso included Seidl's perspective on the interplay of game theory and abstractinterpretation, and Dal Lago's work on a compositional approach to sublinearcomplexity, with interesting connections to functional programming.In the course of the week, approximately half of the talks were devoted tocurrent topics in veriﬁcation, while the other half concerned developments ingame semantics. A variety of topics were covered: Habermehl lectured on regularmodel checking, Leroux talked about about Presburger invariants and Petri-netreachability, Sutre covered the latest results in analyzing pushdown concurrentsystems, Lozes presented the latest work in verifying heap-manipulating pro-grams and Tzevelekos talked about reachability in the functional setting.Concurrency theory featured prominently in several talks. Melliès explainedhow to clarify the connections between game semantics and veriﬁcation by apply-ing ideas from concurrency theory: after recalling the tree-automata techniquesapplied by Ong in order to establish the decidability of mu-calculus formulas onhigher-order recursion schemes, he explained how these techniques are inherentlyconnected to the positionality property of innocent strategies in asynchronousgames. On the veriﬁcation side, Müller-Olm gave a survey of his work on ana-Game Semantics and Program Veriﬁcation 3lyzing threads and procedures, while Zhang talked about verifying probabilisticconcurrent systems. Foundational aspects of model-checking partial-order mod-els in concurrent extensions of the mu-calculus were also discussed by Gutierrez.A number of talks were also concerned with extending the range of gamesemantics to new settings. Levy started with a talk describing how to derivestrategies from programs via transition systems. Then, Laurent gave an overviewof the literature on logic and game semantics, with a special emphasis on thenotion of innocent strategies and its relationship to intuitionistic and classicallogics. Zeilberger developed this direction, and explained how to think of gamesemantics in a purely syntactic way, using extensions of traditional sequent cal-culus. Then, Clairambault discussed calculating least and greatest ﬁxed pointsin game models, while Laird showed his latest results on modelling polymor-phism. Goyet described an extension of the usual syntax of the lambda-calculusin order to obtain a full deﬁnability result for general (not necessarily innocent)strategies on arena games.The atmosphere during the seminar was very good, clearly all the partici-pants were open to new ideas from `the other side'. In particular the introductorytalks attracted a number of questions asking for clariﬁcation on various issues.This showed us as the organizers that people were keen to understand the ma-terial that was presented to them, and that our selection of topics was suitablefor our purposes. The periods we left unscheduled as well as the meals were thenavailable for further discussion. In particular the young researchers present ex-pressed their delight with the opportunity to talk to established participants ina relaxed atmosphere. Because this was a residential workshop, people did nothave to worry about returning to their accommodation, or making arrangementsfor meals, which greatly facilitated smaller groups having additional discussions,of which we saw quite a few.The Dagstuhl staﬀ were extremely helpful throughout the meeting and, be-cause most of the organizational tasks were carried out by them, the participantscould concentrate on scientiﬁc matters. As the organizers we were very gratefulfor all the support! A number of people also commented positively on this aspectin their feedback forms.It is perhaps too early to say how much of an impact our seminar will ulti-mately have. Because for many participants this was the ﬁrst sustained encounterwith the other community, it will take some time for ideas to be digested andadopted. The main achievement of the meeting is the creation of a platform onwhich new collaborations can be built in the years to come, leading to even moresynergy between game semantics and veriﬁcation.TimetableAll lectures took place in Lecture Hall Saarbrücken.4 P.-A. Melliès, A. S. Murawski, A. Schalk and I. WalukiewiczMonday 21st June09:00  09:15Welcome09:15  10:15 Dan Ghica: Game semantics for program veriﬁcationCoffee Break/Discussions10:45  11:45 Andrzej Murawski: Game semantics and automataLunch14:15  15:15 Naoki Kobayashi: Model-checking higher-order programsCoffee Break/Discussions16:00  17:00 Martin Hofmann: Purity of second-order functionalsTuesday 22nd June09:00  10:00 Peter Habermehl: Regular model checking10:00  10:30 Jérôme Leroux: VAS reachability by Presburger inductive invariantsCoffee Break/Discussions11:00  11:45 Grégoire Sutre : Reachability analysis for pushdown concurrent systemsLunch14:00  14:45 Helmut Seidl: Strategy iteration: abstract interpretation meets game theory15:00  15:30 Nikos Tzevelekos: Functional reachabilityCoffee Break/Discussions16:00  16:45 Paul Levy: Operational game semanticsWednesday 23rd June09:00  10:00 Markus Müller-Olm: Optimal analysis of threads and proceduresCoffee Break/Discussions10:15  11:45 Olivier Laurent: Game semantics for logicPaul-André Melliès: : Asynchronous games12:00 Group Photo Session (front of the chapel)LunchExcursionThursday 24th June09:00  10:00 Damian Niwi«ski: A gentle introduction to panic automataNoam Zeilberger: Polarity and double-negation translationCoffee Break/Discussions10:15  11:45 Julian Gutierrez: Model-checking partial-order models of concurrencyLijun Zhang: Concurrency and composition in a stochastic worldLunch14:00  15:30 Pierre Clairambault: Fixed points in gamesJames Laird: Genericity and polymorphismCoffee Break/Discussions16:00  16:45 Ugo Dal Lago: Functional programming in sublinear spaceGame Semantics and Program Veriﬁcation 5Friday 25th June09:15  10:45 Alexis Goyet: Lambda-bar calculusEtienne Lozes: Model-checking the contracts of heap-hopCoffee Break/DiscussionsLunchParticipantsPierre Clairambault (CNRS - Paris)Ugo Dal Lago (Università di Bologna)Ilias Garnier (Commissariat a l'Energie Atomique - Gif-sur-Yvette)Dan Ghica (University of Birmingham)Alexis Goyet (CNRS - Paris)Charles Grellois (ENS - Cachan)Julian Gutierrez (University of Edinburgh)Peter Habermehl (Université Paris Diderot)Martin Hofmann (LMU München)Stefan Kiefer (University of Oxford)Naoki Kobayashi (Tohoku University)James Laird (University of Bath)Olivier Laurent (ENS - Lyon)Jérôme Leroux (Université Bordeaux )Paul Blain Levy (University of Birmingham)Etienne Lozes (ENS - Cachan)Paul-André Melliès (Université Paris Diderot)Markus Müller-Olm (Universität Münster)Andrzej Murawski (University of Oxford)Damian Niwi«ski (Uniwersytet Warszawski)Andrea Schalk (University of Manchester)Helmut Seidl (TU München)Ian Stark (University of Edinburgh)Grégoire Sutre (Université Bordeaux )Nikos Tzevelekos (University of Oxford)Paweª Urzyczyn (Uniwersytet Warszawski)Noam Zeilberger (Université Paris Diderot)Lijun Zhang (Danmarks Tekniske Universitet)

10252 Executive Summary -- Game Semantics and Program Verification

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10252 Executive Summary -- Game Semantics and Program Verification

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