Executive summary

The Confer-2 Working Group follows Basic Research Action CONFER. It is a framework to keep together the CONFER community, and to provide 2 annual workshops.

The overall objective of Confer-2 action is similar to the one of CONFER and to create both the theoretical foundations and the technology for combining the expressive power of the functional and the concurrent computational models. The action is organised around four main areas:

• Foundational Models and Abstract Machines
• Calculi
• Logics for Concurrency and the $\lambda$-calculus
• Programming Languages

(see Periodic Progress Reports of CONFER, for more explanations). In this first year of Confer-2, we may notice the following important and successful facts.

In the area of Foundational Models and Abstract Machines, progress has been done in three areas, there has been a major result by Asperti and Mairson on the non elementary-recursive cost of optimal reductions in the lambda calculus. The work on action calculi has been continued which now provide a uniform setting for dealing with rewrite rules on terms with bound variables. Work on tile models, axiomatic rewrite rules, the sequentiality theorem for the lambda calculus and syntactic transformation of recursive program schemes with non determinism is also part of this section.

In the area of Calculi work has been done at many levels. First, the new blue calculus of Boudol gives a nice language with both the functional and concurrent paradigms. The update-calculus of Parrow and Victor simplifies and extends the $\pi$-calculus, making it suitable also for models with shared states and concurrent constraints. Many results have been obtained to develop new theories for the equivalences of processes, to model concurrent objects or secure communication, or to prove transformations of programs with concurrency.

In the area of Logics for Concurrency and the $\lambda$-calculus, work has proceeded on the development of games semantics for the sequential lambda calculus, linear logic or concurrent processes. Denotational semantics has also been used to give semantics of core Facile.

In the area of Programming Languages several efforts have been completed: a stabilised public release of the PICT language, a first public release of the Join Calculus language, a distributed garbage collector collecting cycles, the design of Linda with localities, an efficient automata-based verification environment for the $\pi$-calculus. Several experiments are also led to investigate the real uses of mobility and agents in programming examples.

As for BRA CONFER, the progress reports in chapter 5 reflect that crossfertilisation of ideas among fellow researchers in the working group is very lively. As in previous years it is evident that related work done at other sites in the consortium is referenced often and also very often used as the basis for development of new results. It is no surprise that a number of these results have been achieved in collaboration between sites, enabled through site visits for shorter or longer periods. Leading researchers outside the consortium have also been involved in fruitful collaborations.

During Year 1 of Confer-2 two workshops have been held.

The working group has produced a large number (about 70) of reports and several of these have been published at conferences, international workshops and journals. Many of theses works are accessible at URL http://www.cs.auc.dk/mobility/, where a Web page on Mobility is maintained by Uwe Nestmann, who moved in September 1997 from INRIA Rocquencourt to Aalborg.

Several Ph.D.'s are in preparation in the action, and several have been defended.