ThisvolumehasitsoriginsinameetingheldatMicrosoftResearch,Cambridge,in April2009tocelebrateTonyHoare's75thBirthday(actually11Jan2009). Allthe technicalpapersexceptforthosewrittenbyAbramsky,Jackson,JonesandMeyer arebased-sometimesclosely,sometimesnot-onpresentationsgivenatthatme- ing. TheideaforthemeetingaroseinconversationsbetweenourselvesandAndrew HerbertofMicrosoft,whohostedatrulymemorableandhappyevent. ThemeetingwasorganisedbyourselvesandKenWood,withthe?nancials- portofMicrosoftResearchandFormalSystems(Europe)Ltd,andheldovertwo days. We wouldlike to recordparticularthanksto Angela Still of Microsoftfor makingallthelocalarrangementsatCambridgeandmuchmore:themeetingwould nothavehappenedwithouther. Whilethemajorityofthepapersinthisvolumearetechnical,weaskedauthorsto re?ectonthein?uenceofHoare'sworkontheirown?eldsandtomakeappropriate remarksonit. Allthetechnicalpaperswererefereed. DiscussionswithWayneWheelerofSpringerinspiredthetwoofustowritethe scienti?cbiographyofHoarethatisthe?rstpaperinthisvolume. Thoughwehave bothknownTonywellformanyyears,wewereamazedathowmanydiscoveries abouthimwemadeduringtheprocessofwritingthisarticle. WewouldlikethankWayneandhisassistantSimonReesfortheirhelpinprep- ingthisvolumeaswellastheirpatience. Muchoftheworkingatheringthepapers, ensuringconsistencyofLaTeXstyles,etc. ,wasdonebyLucyLiofOxfordUniv- sityComputingLaboratoryandwethankherwarmly. Tragically,KenWood'swifeLisadiedafteralongillnessinSeptember2009. Wededicatethisvolumetohermemory. January2010 CliffJones BillRoscoe ix Contents 1 Insight,InspirationandCollaboration...1 C. B. JonesandA. W. Roscoe 2 FromCSPtoGameSemantics...33 SamsonAbramsky 3 OnMereologiesinComputingScience...47 DinesBjorner 4 Roles,Stacks,Histories:ATripleforHoare...71 Johannes Borgstrom, .. Andrew D. Gordon, andRiccardoPucella 5 ForwardwithHoare...101 MikeGordonandHel 'ene ' Collavizza 6 ProbabilisticProgrammingwithCoordination...123 HeJifeng 7 TheOperationalPrincipleandProblemFrames...143 MichaelJackson 8 TheRoleofAuxiliaryVariablesintheFormal DevelopmentofConcurrentPrograms...167 C. B. Jones 9 AvoidaVoid:TheEradicationofNullDereferencing...189 BertrandMeyer,AlexanderKogtenkov,andEmmanuelStapf 10 UnfoldingCSP...213 MikkelBundgaardandRobinMilner xi xii Contents 11 Quicksort:CombiningConcurrency,Recursion, andMutableDataStructures...2 29 DavidKitchin,AdrianQuark,andJayadevMisra 12 TheThousand-and-OneCryptographers...255 A. K. McIverandC. C. Morgan 13 On Process-AlgebraicExtensions of Metric TemporalLogic...283 ChristophHaase,Joel .. Ouaknine,andJamesWorrell 14 FunwithTypeFunctions...301 OlegKiselyov,SimonPeytonJones,andChung-chiehShan 15 OnCSPandtheAlgebraicTheoryofEffects...333 RobvanGlabbeekandGordonPlotkin 16 CSPisExpressiveEnoughfor ...371 A. W. Roscoe 17 TheTokeneerExperiments...405 JimWoodcock,EmineGokc .. ,eAydal,andRodChapman Chapter1 Insight,InspirationandCollaboration C. B. JonesandA. W. Roscoe Abstract TonyHoare'smanycontributionstocomputingsciencearemarkedby insightthatwasgroundedinpracticalprogramming. Manyofhispapershavehada profoundimpactontheevolutionofour?eld;theyhavemoreoverprovidedasource ofinspirationtoseveralgenerationsofresearchers. Weexaminethedevelopmentof hisworkthroughareviewofthedevelopmentofsomeofhismostin?uentialpieces ofworksuchasHoarelogic,CSPandUnifyingTheories. 1. 1 Introduction To many who know Tony Hoare only through his publications, they must often looklikepolishedgemsthatcomefromamindthatrarelymakesfalsesteps,nor evenperhapshastoworkattheircreation. Assooften,thisimpressionisafurther complimenttosomeonewhoactuallyaddstoveryhardworkandmanydiscarded attempts the ?nal polish thatmakes complexideas relatively easy for the reader tocomprehend. Asindicatedonpagexiof[HJ89],hisideastypicallygothrough manyrevisions. ThetwoauthorsofthecurrentpapereachhadthehonourofTonyHoaresuperv- ingtheirdoctoralstudiesinOxford. Theyknowat?rsthandhiskindandgenerous styleandwillcountitasanachievementifthispapercanconveysomethingofthe workingmethodsofsomeonebigenoughtoeschewcompetitionandpointscoring. Indeedit willbe apparentfromthe followingsectionshowoften,havingstarted somenewwayofthinkingorexcitingideas,hehappilyleavestheirexplorationand developmenttoothers. Wehavebothbene?tedpersonallyfromthis. C. B. Jones( ) SchoolofComputingScience,NewcastleUniversity,UK e-mail:cliff. jones@ncl. ac. uk A. W. Roscoe OxfordUniversityComputingLaboratory,UK e-mail:Bill. Roscoe@comlab. ox. ac. uk C. B. Jonesetal. (eds. ),Re?ectionsontheWorkofC. A. R.

CSP notation has been used extensively for teaching and applying concurrency theory, ever since the publication of the text Communicating Sequential Processes by C.A.R. Hoare in 1985. Both a programming language and a specification language, the theory of CSP helps users to understand concurrent systems, and to decide whether a program meets its specification. As a member of the family of process algebras, the concepts of communication and interaction are presented in an algebraic style. An invaluable reference on the state of the art in CSP, Understanding Concurrent Systems also serves as a comprehensive introduction to the field, in addition to providing material for a number of more advanced courses. A first point of reference for anyone wanting to use CSP or learn about its theory, the book also introduces other views of concurrency, using CSP to model and explain these. The text is fully integrated with CSP-based tools such as FDR, and describes how to create new tools based on FDR. Most of the book relies on no theoretical background other than a basic knowledge of sets and sequences. Sophisticated mathematical arguments are avoided whenever possible. Topics and features: presents a comprehensive introduction to CSP; discusses the latest advances in CSP, covering topics of operational semantics, denotational models, finite observation models and infinite-behaviour models, and algebraic semantics; explores the practical application of CSP, including timed modelling, discrete modelling, parameterised verifications and the state explosion problem, and advanced topics in the use of FDR; examines the ability of CSP to describe and enable reasoning about parallel systems modelled in other paradigms; covers a broad variety of concurrent systems, including combinatorial, timed, priority-based, mobile, shared variable, statecharts, buffered and asynchronous systems; contains exercises and case studies to support the text; supplies further tools and information at the associated website: http://www.comlab.ox.ac.uk/ucs/. From undergraduate students of computer science in need of an introduction to the area, to researchers and practitioners desiring a more in-depth understanding of theory and practice of concurrent systems, this broad-ranging text/reference is essential reading for anyone interested in Hoare's CSP.

ThisvolumehasitsoriginsinameetingheldatMicrosoftResearch,Cambridge,in April2009tocelebrateTonyHoare's75thBirthday(actually11Jan2009). Allthe technicalpapersexceptforthosewrittenbyAbramsky,Jackson,JonesandMeyer arebased-sometimesclosely,sometimesnot-onpresentationsgivenatthatme- ing. TheideaforthemeetingaroseinconversationsbetweenourselvesandAndrew HerbertofMicrosoft,whohostedatrulymemorableandhappyevent. ThemeetingwasorganisedbyourselvesandKenWood,withthe?nancials- portofMicrosoftResearchandFormalSystems(Europe)Ltd,andheldovertwo days. We wouldlike to recordparticularthanksto Angela Still of Microsoftfor makingallthelocalarrangementsatCambridgeandmuchmore:themeetingwould nothavehappenedwithouther. Whilethemajorityofthepapersinthisvolumearetechnical,weaskedauthorsto re?ectonthein?uenceofHoare'sworkontheirown?eldsandtomakeappropriate remarksonit. Allthetechnicalpaperswererefereed. DiscussionswithWayneWheelerofSpringerinspiredthetwoofustowritethe scienti?cbiographyofHoarethatisthe?rstpaperinthisvolume. Thoughwehave bothknownTonywellformanyyears,wewereamazedathowmanydiscoveries abouthimwemadeduringtheprocessofwritingthisarticle. WewouldlikethankWayneandhisassistantSimonReesfortheirhelpinprep- ingthisvolumeaswellastheirpatience. Muchoftheworkingatheringthepapers, ensuringconsistencyofLaTeXstyles,etc. ,wasdonebyLucyLiofOxfordUniv- sityComputingLaboratoryandwethankherwarmly. Tragically,KenWood'swifeLisadiedafteralongillnessinSeptember2009. Wededicatethisvolumetohermemory. January2010 CliffJones BillRoscoe ix Contents 1 Insight,InspirationandCollaboration...1 C. B. JonesandA. W. Roscoe 2 FromCSPtoGameSemantics...33 SamsonAbramsky 3 OnMereologiesinComputingScience...47 DinesBjorner 4 Roles,Stacks,Histories:ATripleforHoare...71 Johannes Borgstrom, .. Andrew D. Gordon, andRiccardoPucella 5 ForwardwithHoare...101 MikeGordonandHel 'ene ' Collavizza 6 ProbabilisticProgrammingwithCoordination...123 HeJifeng 7 TheOperationalPrincipleandProblemFrames...143 MichaelJackson 8 TheRoleofAuxiliaryVariablesintheFormal DevelopmentofConcurrentPrograms...167 C. B. Jones 9 AvoidaVoid:TheEradicationofNullDereferencing...189 BertrandMeyer,AlexanderKogtenkov,andEmmanuelStapf 10 UnfoldingCSP...213 MikkelBundgaardandRobinMilner xi xii Contents 11 Quicksort:CombiningConcurrency,Recursion, andMutableDataStructures...2 29 DavidKitchin,AdrianQuark,andJayadevMisra 12 TheThousand-and-OneCryptographers...255 A. K. McIverandC. C. Morgan 13 On Process-AlgebraicExtensions of Metric TemporalLogic...283 ChristophHaase,Joel .. Ouaknine,andJamesWorrell 14 FunwithTypeFunctions...301 OlegKiselyov,SimonPeytonJones,andChung-chiehShan 15 OnCSPandtheAlgebraicTheoryofEffects...333 RobvanGlabbeekandGordonPlotkin 16 CSPisExpressiveEnoughfor ...371 A. W. Roscoe 17 TheTokeneerExperiments...405 JimWoodcock,EmineGokc .. ,eAydal,andRodChapman Chapter1 Insight,InspirationandCollaboration C. B. JonesandA. W. Roscoe Abstract TonyHoare'smanycontributionstocomputingsciencearemarkedby insightthatwasgroundedinpracticalprogramming. Manyofhispapershavehada profoundimpactontheevolutionofour?eld;theyhavemoreoverprovidedasource ofinspirationtoseveralgenerationsofresearchers. Weexaminethedevelopmentof hisworkthroughareviewofthedevelopmentofsomeofhismostin?uentialpieces ofworksuchasHoarelogic,CSPandUnifyingTheories. 1. 1 Introduction To many who know Tony Hoare only through his publications, they must often looklikepolishedgemsthatcomefromamindthatrarelymakesfalsesteps,nor evenperhapshastoworkattheircreation. Assooften,thisimpressionisafurther complimenttosomeonewhoactuallyaddstoveryhardworkandmanydiscarded attempts the ?nal polish thatmakes complexideas relatively easy for the reader tocomprehend. Asindicatedonpagexiof[HJ89],hisideastypicallygothrough manyrevisions. ThetwoauthorsofthecurrentpapereachhadthehonourofTonyHoaresuperv- ingtheirdoctoralstudiesinOxford. Theyknowat?rsthandhiskindandgenerous styleandwillcountitasanachievementifthispapercanconveysomethingofthe workingmethodsofsomeonebigenoughtoeschewcompetitionandpointscoring. Indeedit willbe apparentfromthe followingsectionshowoften,havingstarted somenewwayofthinkingorexcitingideas,hehappilyleavestheirexplorationand developmenttoothers. Wehavebothbene?tedpersonallyfromthis. C. B. Jones( ) SchoolofComputingScience,NewcastleUniversity,UK e-mail:cliff. jones@ncl. ac. uk A. W. Roscoe OxfordUniversityComputingLaboratory,UK e-mail:Bill. Roscoe@comlab. ox. ac. uk C. B. Jonesetal. (eds. ),Re?ectionsontheWorkofC. A. R.

CSP notation has been used extensively for teaching and applying concurrency theory, ever since the publication of the text Communicating Sequential Processes by C.A.R. Hoare in 1985. Both a programming language and a specification language, the theory of CSP helps users to understand concurrent systems, and to decide whether a program meets its specification. As a member of the family of process algebras, the concepts of communication and interaction are presented in an algebraic style. An invaluable reference on the state of the art in CSP, Understanding Concurrent Systems also serves as a comprehensive introduction to the field, in addition to providing material for a number of more advanced courses. A first point of reference for anyone wanting to use CSP or learn about its theory, the book also introduces other views of concurrency, using CSP to model and explain these. The text is fully integrated with CSP-based tools such as FDR, and describes how to create new tools based on FDR. Most of the book relies on no theoretical background other than a basic knowledge of sets and sequences. Sophisticated mathematical arguments are avoided whenever possible. Topics and features: presents a comprehensive introduction to CSP; discusses the latest advances in CSP, covering topics of operational semantics, denotational models, finite observation models and infinite-behaviour models, and algebraic semantics; explores the practical application of CSP, including timed modelling, discrete modelling, parameterised verifications and the state explosion problem, and advanced topics in the use of FDR; examines the ability of CSP to describe and enable reasoning about parallel systems modelled in other paradigms; covers a broad variety of concurrent systems, including combinatorial, timed, priority-based, mobile, shared variable, statecharts, buffered and asynchronous systems; contains exercises and case studies to support the text; supplies further tools and information at the associated website: http://www.comlab.ox.ac.uk/ucs/. From undergraduate students of computer science in need of an introduction to the area, to researchers and practitioners desiring a more in-depth understanding of theory and practice of concurrent systems, this broad-ranging text/reference is essential reading for anyone interested in Hoare's CSP.

Since techniques from topology and category theory have been used increasingly by theoretical computer scientists in recent years, it was decided during the Oxford Topology Symposium to hold a special session which would be devoted to the application of these topics in computer science. By holding this session in the context of the topology symposium, the organizers hoped to achieve a cross-fertilization between the communities they brought together - providing mathematicians with a course of new problems with a more practical flavour, and computer scientists with a source of solutions and ideas.