A systematic analysis of trace- and failure-based compositional semantic models for Basic LOTOS is presented. The analysis is motivated by the fact that the weakest known equivalences preserving sufficient information for several typical verification tasks are failure-based, and the weakness of an equivalence can be advantageous for verification. Both the equivalences and the preorders corresponding to the semantic models are covered. The analysis yields in a natural way two compositional semantic models, which are particularly suited for the verification of a general class of liveness properties, a task which cannot be performed with most established models.

Abstract.A result quantity in a numerical algorithm is considered as a function of the input data, roundoff and truncation errors. In order to investigate this functional relationship using the methods of mathematical analysis a structural model of the numerical algorithm called R-automaton is introduced. It is shown that the functional dependence defined by an R-automaton is a continuous rational function in a neighborhood of any data point except in a point set, the Lebesgue measure of which is zero. An effective general-purpose algorithm is presented to compute the derivative of any result quantity with respect to the individual roundoff and truncation errors. Some ways of generalizing the R-automaton model without losing the results achieved are finally suggested.Introduction.

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Modern cellular telephone systems extend the usability of portable personal computers enormously. A nomadic user can be given ubiquitous access to remote information stores and computing services. However, the behavior of wireless links creates severe inconveniences within the traditional data communication paradigm. In this paper we give an overview of the problems related to wireless mobility. We also present a new software architecture for mastering them and discuss a new paradigm for designing mobile distributed applications. The key idea in the architecture is to place a mediator, a distributed intelligent agent, between the mobile node and the wireline network. A prototype implementation of the architecture exists in an environment consisting of Linux and Windows platforms and the GSM cellular telephone network.

voI{ MARTTI TIENARIWi,rd,, m,it Geneltm,igung der Mathemat'isch-I{aturw'issenschaJtl'ichen Selct'ion, der Ph,,ilosoph,iscluen, Ealcuhat der f|n'iuers'itat Hels'ink'i a,n?, 75.September 1962 urn 12 Uhrim Aud'itorium Porthan'ia III zur öffentlichen V erte'idi,gung uorgelegt.