SoSL was the first International Workshop on Semantics of Specification Languages, held from 25-27 October 1993 in Utrecht, the Netherlands. The workshop was organized by the Department of Philosophy of Utrecht University with financial support from the Nationale Faciliteit Informatica of the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), and under the auspices of the British Computer Society'S specialist group in Formal Aspects of Computing Science (BCS FACS). The concern of the workshop was the semantics of specification languages, and the issues closely related to this area, such as type checking and the justification of proof rules and proof obligations. Its aim was the exchange of problems and ideas in this field of formal methods, and the identification of common programs of work for further investigation. The program of SoSL consisted of 3 invited lectures presenting the developments of the semantics of 3 major specification languages. Furthermore, there were 16 presentations of submitted papers. This volume provides a direct account of the workshop. It contains 3 papers that match the invited lectures and the 16 selected papers. The editors want to thank all those who have contributed to the workshop; the Program Committee and the referees for selecting the contributed papers, the invited speakers for their interesting talks, the Organizing Committee for all their efforts, and of course the participants. We have the feeling that the workshop was worthwhile and should be repeated.

The lambda calculus was developed in the 1930s by Alonzo Church. The calculus turned out to be an interesting model of computation and became theprototype for untyped functional programming languages. Operational and denotational semantics for the calculus served as examples for otherprogramming languages. In typed lambda calculi, lambda terms are classified according to their applicative behavior. In the 1960s it was discovered that the types of typed lambda calculi are in fact appearances of logical propositions. Thus there are two possible views of typed lambda calculi: - as models of computation, where terms are viewed as programs in a typed programming language; - as logical theories, where the types are viewed as propositions and the terms as proofs. The practical spin-off from these studies are: - functional programming languages which are mathematically more succinct than imperative programs; - systems for automated proof checking based on lambda caluli. This volume is the proceedings of TLCA '93, the first international conference on Typed Lambda Calculi and Applications, organized by the Department of Philosophy of Utrecht University. It includes29 papers selected from 51 submissions.

CONCUR'91 is the second international conference on concurrency theory, organized in association with the NFI project Transfer. It is a sequel to the CONCUR'90 conference. Its basic aim is to communicate ongoing work in concurrency theory. This proceedings volume contains 30 papers selected for presentation at the conference (from 71 submitted) together with four invited papers and abstracts of the other invited papers. The papers are organized into sections on process algebras, logics and model checking, applications and specification languages, models and net theory, design and real-time, tools and probabilities, and programming languages. The proceedings of CONCUR'90 are available asVolume 458 of Lecture Notes in Computer Science.