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284 Process Part of POOSL relations. Especially in the context of behaviour-preserving transformations, this is a very pleasant property. Another appealing property of observation equivalence is that it benefits from the simple proof technique of finding so-called bisimulations. A bisimulation establishes a kind of invariant holding between a pair of dynamic systems, and the technique is to prove two systems equivalent by establishing such an invariant. Bisimulations are particularly useful if the semantics is given in an operational way (as in the case of POOSL). The notion of bisimulation was first introduced by Park in [Par81] and later developed in the context of CCS in [Mil83]. We start defining observation equivalence in terms of weak bisimulations. We then slightly refine observation equivalence to obtain transformation equivalence. A binary relation over configurations (conf p 1 ¥ conf p 2 ) implies (i) the Sys parts of conf p 1 and conf p 2 are syntactically identical and for all a ¡ Act (ii) if conf p 1 (iii) if conf p 2 Here, £ a conf p 1 ¡ then, for some conf p 2 ¡ , conf p 2 a conf £ p 2 ¡ then, for some conf p 1 ¡ , conf p 1 ¥ Conf p Conf p is a weak bisimulation if ¡ ¤ a conf p 2 ¡ and (conf p 1 ¡ conf ¥ p 2 ¡ ¡ ) ¡ a conf ¤ p 1 ¡ and (conf p 1 ¡ conf ¥ p 2 ¡ ¡ ) ¡ ¤ a is a binary transition relation over configurations (often called descendant relation). Let conf p 1 , conf p 2 be configurations and let l be a communication action. Then conf p 1 conf p 1 ¡ ¤ l 2 conf p 2 if conf p ¡ conf ¤ p p if conf1 ( £ ) conf p 2 1 £ ( ) l £ ( £ ) conf p 2 Our notion of weak bisimulation is very similar to that of CCS [Mil80]. The difference is that CCS does not include (i) in its definition. We, however, need to incorporate (i) to insure that every data class name referred to by any send or receive action, unambiguously denotes a single class. Observation equivalence ( ¢ ) on configurations is defined in terms of weak bisimulations. Configurations conf p 1 and conf p 2 are observation equivalent, written conf p 1 conf p 2 ) ¡ for some weak bisimulation . So ¢ . conf p 2 , if (conf p 1 , £ ¡ is a weak bisimulation ¦ ¢ ¨ Note that since every POOSL specification is also a configuration, weak bisimulations and observation equivalence are defined on specifications too. Although observation equivalence reflects a very strong notion of equivalence, it is branching equivalence [vGW96].
9.6 Example: A Simple Handshake Protocol 285 slightly too weak for our purposes. Suppose some system is specified in POOSL, and assume an interactive simulation of this system is being performed. It could happen that in order to compare different system architectures, the system needs to be transformed during simulation. Although the structures of the systems before and after the transformation differ, their functional behaviour is indistinguishable. Now a problem may arise if the simulation is reset. It would be convenient if the functional behaviour of the reset system after simulation was still equivalent to the behaviour of the reset system before the transformation. Unfortunately, this cannot be guaranteed, at least not if observation equivalence is applied as behaviour equivalence. The reason is that observation equivalence only refers to future behaviour of systems, and does not state anything about their past. The solution to the problem is to define a slightly stronger relation which takes the past behaviour of systems into account. Our new relation is called transformation equivalence . Configurations conf p 1 and conf p 2 are transformation equivalent, written conf p 1 if and only if (i) conf p 1 ¢ conf p 2 (ii) Reset(conf p 1 ) ¢ Reset(conf p 2 ) ¢ ¡ conf p 2 , So, two configurations are transformation equivalent if they are observation equivalent and if they are still observation equivalent after they both have been reset. The Reset of a configuration is the corresponding initial behaviour specification, i.e., the system specification from which it is (probably) derived (see also Subsection 9.5.2). Now that we have defined relation ¢ £¢¥¤ ¡ ¡ we will define a semantic function that assigns a meaning to each configuration (and thus implicitly to each system specification). Since ¢ ¡ is an equivalence relation (this is proved in Chapter 10), we can consider the meaning of a configuration to be the class of all transformation equivalent configurations. Let conf p ¡ Conf p . Then £¢¥¤ (conf p ) § conf p £¢¥¤ § where conf p p £¢¥¤ denotes the set of all configuration from Conf that are transformation equivalent to conf p . Evidently, £¢¥¤ (conf p £¢¥¤ p 1 ) (conf2 ) if and only if conf p 1 ¡ conf p 2 , so, two config- ¢ urations are transformation equivalent, precisely if they have the same semantics. 9.6 Example: A Simple Handshake Protocol In this section we will show how to calculate the behaviour of a simple handshake protocol, using the labeled-transition system defined in Subsection 9.5.3. Further, we
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Specification of Reactive Hardware/
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to Leny, Inge and our parents
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Contents Acknowledgements v 1 Intro
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CONTENTS ix 4.6.5 Aggregate Semanti
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CONTENTS xi 6 Modelling of Concurre
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CONTENTS xiii 6.6.7.2 System Specif
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CONTENTS xv 11.4.2.3 Requirements C
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List of Figures 1.1 Chapter Overvie
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LIST OF FIGURES xix 6.16 Strongly D
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Chapter 1 Introduction 1.1 Objectiv
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1.1 Objectives 3 understood and sti
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1.1 Objectives 5 Informal and Forma
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1.2 Thesis Organisation 7 Chapter 1
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1.2 Thesis Organisation 9 Recommend
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Chapter 2 On Specification of React
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2.3 Specifications, Models and View
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2.4 Specification Languages, Formal
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2.4 Specification Languages, Formal
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2.5 Modelling Concepts 23 entirety.
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2.5 Modelling Concepts 25 Tradition
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2.6 Activity Frameworks for Specifi
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2.6 Activity Frameworks for Specifi
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2.7 Summary 31 offer many guideline
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Chapter 3 Concepts for Analysis, Sp
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3.3 Concepts 35 3. creation of a sy
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3.5 Combining Compatible Concepts 3
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3.6 Practical Use of Concepts 39 3.
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3.6 Practical Use of Concepts 41 Th
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3.6 Practical Use of Concepts 43 ac
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3.6 Practical Use of Concepts 45 ac
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3.6 Practical Use of Concepts 47 wa
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3.6 Practical Use of Concepts 49 Ge
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3.6 Practical Use of Concepts 51 Re
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3.7 Summary and Concluding Remarks
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Chapter 4 Abstraction of a Problem
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4.1 Introduction 57 earlier phase t
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4.2 Objects 59 An object can mean t
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4.2 Objects 61 wonder what other ob
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4.3 Classes 63 A message interface
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4.3 Classes 65 Class B Attributes M
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4.4 Data Objects and Process Object
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4.5 Clusters 79 flows. Clusters ena
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4.6 Aggregates 81 Therefore a compl
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4.6 Aggregates 83 4.6.4 Clustered A
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4.6 Aggregates 85 An old philosophi
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4.7 Identity and Object Identifiers
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4.8 Properties of Composites 89 for
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4.8 Properties of Composites 91 com
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4.8 Properties of Composites 93 Whe
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4.8 Properties of Composites 95 In
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4.9 Channel Hiding 97 Servant A Sup
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4.11 Composites and Hierarchies 99
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4.12 Object Variety 101 Part class
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4.13 Object Class Models 103 Anothe
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4.13 Object Class Models 105 of obj
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4.14 Attributes and Variables 107 c
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4.14 Attributes and Variables 109 4
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4.15 Operations, Services, Methods
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4.15 Operations, Services, Methods
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4.17 Summary 115 Accidental Propert
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Chapter 5 Concepts for the Integrat
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5.2 Architecture 119 Requirements D
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5.3 Design Philosophy 121 this. The
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5.4 Essential Model and Extended Mo
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5.4 Essential Model and Extended Mo
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5.6 Architecture and Implementation
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5.7 Views 129 Management £ £ £ P
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5.7 Views 131 Behaviour Behaviour U
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5.8 Boundaries 133 5.8 Boundaries 5
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5.8 Boundaries 135 x x Object A y z
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5.8 Boundaries 137 x w w x Object A
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5.8 Boundaries 139 In Chapter 10 we
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5.9 Transformations 141 The modific
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5.10 Formalisation 143 Level 1 Leve
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5.11 Summary 145 Behaviour Requirem
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Chapter 6 Modelling of Concurrent R
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6.2 Concurrency and Synchronisation
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6.3 Communication 157 between proce
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6.3 Communication 159 or to transfo
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6.3 Communication 161 6.3.3.4 Messa
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6.3 Communication 163 Synchronous m
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6.3 Communication 165 channel-name
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6.3 Communication 167 can be descri
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6.3 Communication 169 statement aft
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6.3 Communication 171 (normalCourse
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6.3 Communication 173 ∞ client re
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6.3 Communication 175 There is a gr
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6.3 Communication 177 process A pro
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6.3 Communication 179 Clocks An int
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6.3 Communication 181 whether the s
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6.3 Communication 183 6.3.9.4 Model
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6.3 Communication 185 6.3.10.2 Desc
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6.4 Distribution 187 force to take
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6.4 Distribution 189 is that the in
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6.4 Distribution 191 links to each
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6.4 Distribution 193 6.4.6 Distribu
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6.5 Scenarios 195 entities. This su
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6.5 Scenarios 197 startJob readyToA
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6.5 Scenarios 199 collection of tex
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6.6 Dynamic Behaviour 201 selection
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6.6 Dynamic Behaviour 203 processes
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6.6 Dynamic Behaviour 205 even for
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6.6 Dynamic Behaviour 207 with the
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6.6 Dynamic Behaviour 209 6.6.4 Sep
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6.6 Dynamic Behaviour 211 6.6.5 Mod
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6.6 Dynamic Behaviour 213 to pay at
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6.6 Dynamic Behaviour 215 A method
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6.6 Dynamic Behaviour 217 to happen
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6.6 Dynamic Behaviour 219 c a Multi
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6.6 Dynamic Behaviour 221 but not t
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6.7 Real-Time Modelling 223 claimed
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6.7 Real-Time Modelling 225 in the
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6.8 Summary 227 They can graphicall
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Chapter 7 Introduction to the Seman
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7.2 A Brief Language Characterisati
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Page 255 and 256: 7.4 Mathematical Preliminaries 235
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Page 259 and 260: 7.5 Concluding Remarks 239 0 ¡ Bin
Page 261 and 262: Chapter 8 Data Part of POOSL Chapte
Page 263 and 264: 8.3 Formal Syntax 243 runk, and cun
Page 265 and 266: 8.4 Context Conditions 245 Further,
Page 267 and 268: 8.5 A Computational Semantics 247 T
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Page 273 and 274: 8.6 Primitive deepCopy Messages 253
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Page 277 and 278: 8.7 Example: Complex Numbers 257 is
Page 279 and 280: 8.8 Summary and Concluding Remarks
Page 281 and 282: Chapter 9 Process Part of POOSL Cha
Page 283 and 284: 9.3 Formal Syntax 263 In almost any
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Page 311 and 312: 9.7 The Development of POOSL 291 is
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Page 315 and 316: 9.7 The Development of POOSL 295 e
Page 317 and 318: 9.7 The Development of POOSL 297 Em
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Page 321 and 322: 9.8 Summary 301 To prepare the deve
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Page 325 and 326: 10.2 Instance Structure Diagrams 30
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Page 351 and 352: 10.8 Summary 331 are transformation
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11.2 SHE Context and Phases 335 Inf
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11.2 SHE Context and Phases 337 a p
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11.2 SHE Context and Phases 339 11.
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11.3 SHE Framework 341 the system.
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11.4 Essential Specification Modell
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11.5 Extended Specification Modelli
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Chapter 12 Case Study Chapter 1 Cha
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12.2 Initial Requirements Descripti
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12.3 The Essential Specification 37
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12.4 Towards an Extended Specificat
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12.5 Concluding Remarks 399 i1 DIST
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12.5 Concluding Remarks 401 Feeder
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Chapter 13 Conclusions and Future W
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13.2 P.H.A. van der Putten’s Cont
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13.2 P.H.A. van der Putten’s Cont
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13.4 Related Results 409 The notion
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Appendix A The POOSL Transition Sys
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A.1 The Data Part of POOSL 413 (12)
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A.2 The Process Part of POOSL 415 A
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A.2 The Process Part of POOSL 417 (
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A.2 The Process Part of POOSL 419 (
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A.2 The Process Part of POOSL 421 i
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Appendix B Proofs of Propositions a
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Proofs of Propositions and Transfor
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Appendix C Glossary of Symbols This
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Glossary of Symbols 437 267 Cp ¥¡
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References [AB90] P. America and F.
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REFERENCES 441 [C [C [C 86] B. Cohe
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REFERENCES 443 [Her90] A.J.H. Herbe
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REFERENCES 445 [MV93] S. Mauw and G
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REFERENCES 447 [vE89] P. van Eijk.
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Index abort, 297 abstract action so
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INDEX 451 strong, 190, 293 subsyste
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INDEX 453 delay, 178 do-statement,
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Summary This combined thesis descri
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Samenvatting Dit gecombineerde proe
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Curricula Vitae Piet van der Putten
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