We present a new kind of ambient calculus in which the open capability is replaced by direct mobility of generic processes. The calculus comes equipped with a labelled transition system in which types play a major role: this system allows us to show interesting algebraic laws. As usual, types express the communication, access and mobility properties of the modelled system, and inferred types express the minimal constraints required for the system to be well behaved.

This paper presents a short survey of some recent approaches relating two different areas, viz. deterministic chaos and computability. Chaos in classical physics may be approached by dynamical (equationally determined) systems or stochastic ones (as random processes). However, randomness has also been effectively modelled using recursion theoretic tools by P. Martin-Löf. We recall its connections to Kolmogorov complexity and show some applications to dynamical systems. This allows us to introduce results that connect well-established notions of entropy and algorithmic information.

In this paper we characterise the equivalential reducts of classical and intuitionistic logics over a language with two propositional variables. We then investigate the size of the fraction of the tautologies of these logics against all formulas. Some methods from complex analysis are used to achieve this goal.

We explore the way in which the refinement of individual ‘local’ components of a specification relates to the development of a ‘global’ system from a specification of requirements. The observational interpretation of specifications and refinements adds expressive power and flexibility, but introduces some subtle problems. Our study of these issues is carried out in the context of Casl architectural specifications. We introduce a definition of observational equivalence for Casl models, leading to an observational semantics for architectural specifications for which we prove important properties. Overall, this fulfills the long-standing goal of complementing the standard semantics of Casl specifications with an observational view that supports observational refinement of specifications in combination with Casl-style architectural design.

We model micro-architectures with non-pipelined instruction processing and pipelined instruction processing using Maurer machines, basic thread algebra and program algebra. We show that stored programs are executed as intended with these micro-architectures. We believe that this work provides a new mathematical approach to the modelling of micro-architectures and the verification of their correctness and the anticipated speed-up results.

We present a new data structure, called a Decomposition Tree (DT), for analysing Boolean functions, and demonstrate a variety of applications. In each node of the DT, appropriate bit-string decomposition fragments are combined by a logical operator. The DT has 2k nodes in the worst case, which implies exponential complexity for problems where the whole tree has to be considered. However, it is important to note that many problems are simpler. We show that these can be handled in an efficient way using the DT. Nevertheless, many problems are of exponential complexity and cannot be made any simpler: for example, the calculation of prime implicants. Using our general DT structure, we present a new worst case algorithm to compute all prime implicants. This algorithm has a lower time complexity than the well-known Quine–McCluskey algorithm and is the fastest corresponding worst case algorithm so far.