We study extensions of the process algebra axiom system ACP with two recursive operations: the binary Kleene star ∗, which is defined by x ∗ y = x(x ∗y) + y, and the push-down operation $, defined by x $ y = x((x $ y)(x $ y)) + y. In this setting it is easy to represent register machine computation, and an equational theory results that is not decidable. In order to increase the expressive power, abstraction is then added: with rooted branching bisimulation equivalence each computable process can be expressed, and with rooted τ-bisimilarity each semi-computable process that initially is finitely branching can be expressed. Moreover, with abstraction and a finite number of auxiliary actions these results can be obtained without binary Kleene star. Finally, we consider two alternatives for the push-down operation. Each of these gives rise to similar results.

CWI is a founding member of ERCIM, the European Research Consortium for Informatics and Mathematics. CWI's research has a theme-oriented structure and is grouped into four clusters. Listed below are the names of the clusters and in parentheses their acronyms.

Abstract. The SANE Virtual Processor (SVP) is a fine-grain, threadbased model of concurrent program composition developed and used at the University of Amsterdam as a basis for designing and programming many-core chips. Its design goal was to support dynamic concurrency and hence support self-adaptive systems within the AETHER collaborative European project. It provides an effective solution for programming chip multiprocessor systems [11, 12, 17]. In this paper, we take thread algebra [10], a semantics for recent object-oriented programming languages such as C # and Java, as a theoretical framework to the verification and evaluation of SVP. We show how a SVP program behavior can be determined in TAsvp, an extension of thread algebra with the features of SVP, and prove that SVP programs satisfy the determinism property, i.e. the programs always give the same result, a key property of the sequential paradigm that SVP will replace.

We study one of the many aspects of privacy, which is referred to as data anonymity, in a formal context. Data anonymity expresses whether some piece of observed data, such as a vote, can be attributed to a user, in this case a voter. We validate the formal treatment of data anonymity by analyzing a well-known electronic voting protocol.

Monads have become a fundamental tool for structuring denotational semantics and programs by abstracting a wide variety of computational features such as side-effects, input/output, exceptions, continuations and non-determinism. In this setting, the notion of a monad is equipped with operations that allow programmers to manipulate these computational effects. For example, a monad for side-effects is equipped with operations for setting and reading the state, and a monad for exceptions is equipped with operations for throwing and handling exceptions. When several effects are involved, one can employ the incremental approach to modular monadic semantics, which uses monad transformers to build up the desired monad one effect at a time. However, a limitation of this approach is that the effect-manipulating operations need to be manually lifted to the resulting monad, and consequently, the lifted operations are non-uniform. Moreover, the number of liftings needed in a system grows as the product of the number of monad transformers and operations involved. This dissertation proposes a theory of uniform lifting of operations that extends the incremental approach to modular monadic semantics with a principled technique for lifting operations. Moreover the theory is generalized from monads to monoids in a monoidal category, making it possible to apply it to structures other than monads. The extended theory is taken to practice with the implementation of a new extensible monad transformer library in Haskell, and with the use of modular monadic semantics to obtain modular operational semantics. i No hay ejercicio intelectual que no sea finalmente inútil. Una doctrina es al principio una descripción verosímil del universo; giran los años y es un mero capítulo—cuando no un párrafo o un nombre—de la historia de la filosofía. There is no exercise of the intellect which is not, in the final analysis, useless. A philosophical doctrine begins as a plausible description of the universe; with the passage of the years it becomes a mere chapter—if not a paragraph or a name—in the history of philosophy.

Abstract. In these lectures we will introduce an interactive system that supports writing simple functional programs. Using this system, students learning functional programming: – develop their programs incrementally, – receive feedback about whether or not they are on the right track, – can ask for a hint when they are stuck, – see how a complete program is stepwise constructed, – get suggestions about how to refactor their program. The system itself is implemented as a functional program, and uses fundamental concepts such as rewriting, parsing, strategies, program transformations and higher-order combinators such as the fold. We will introduce these concepts, and show how they are used in the implementation of the interactive functional programming tutor. 1

Abstract. This paper presents a formal approach to the verification and evaluation of a programming/machine model being developed at the University of Amsterdam, called the SANE Virtual Processor (SVP). The model is being used as a basis for designing and programming chip multiprocessors and to support self-adaptive computation. This model can provide solutions for effectively programming distributed multiprocessor systems [12, 13, 17]. We take thread algebra [11], a semantics for recent object-oriented programming languages such as C # and Java, as a theoretical framework of our approach. We model the basic interleaving strategies used in SVP, and show in thread algebra that the SVP programs has a desired property, i.e. they are communication-deadlock free. 1

Abstract. We present a first-order extension of the algebraic theory about processes known as ACP and its main models. Useful predicates on processes, such as deadlock freedom and determinism, can be added to this theory through first-order definitional extensions. Model theory is used to analyse the discrepancies between identity in the models of the first-order extension of ACP and bisimilarity of the transition systems extracted from these models, and also the discrepancies between deadlock freedom in the models of a first-order definitional extension of this theory and deadlock freedom of the transition systems extracted from these models. First-order definitions are material to the formalization of an interpretation of one theory about processes in another. We give a comprehensive example of such an interpretation too.

Constraint automata have been used as an operational model for Reo which o#ers a channel-based framework to compose complex component connectors. In this paper, we introduce a variant of constraint automata with discrete probabilities and nondeterminism, called probabilistic constraint automata. These can serve for compositional reasoning about connector components, modelled by Reo circuits with unreliable channels, e.g., that might loose or corrupt messages, or channels with random output values that, e.g., can be helpful to model randomized coordination principles.

Over the last two decades formal methods have been extended towards performance and reliability evaluation. This paper tries to provide a rather intuitive explanation of the basic concepts and features in this area. Instead of striving for mathematical rigour, the intention is to give an illustrative introduction to the basics of stochastic models, to stochastic modelling using process algebra, and to model checking as a technique to analyse stochastic models.