## Section: New Results

### Languages and Foundations: Process algebra

Participants : Damien Pous, Alan Schmitt, Jean-Bernard Stefani, Claudio Mezzina, Cinzia di Giusto.

The goal of this work is to study process algebraic foundations for component-based programming. Because of the inherently higher-order character of dynamic configuration operations (modelled e.g. by the passivation construct of the Kell calculus [100] ), we are led to study new techniques for proving program equivalence in higher-order calculi, to develop new forms of bisimulation, and to study the expressivity of different constructs in higher-order calculi.

In our ongoing collaboration with the INRIA Focus team lead by Davide Sangiorgi at the University of Bologna, we have continued exploring the expressive power of the higher-order pi-calculus. In particular, we have shown that the biadic variant of the calculus is strictly more expressive than the monadic variant [39] .

Early in 2010, Sergueï Lenglet has successfully defended his PhD thesis [16] , where he has shown the first characterization of weak contextual equivalence for calculi with passivation and applied it to the Seal and Kell calculi.

In our collaboration with the Plume team at LIP (Daniel Hirschkoff) we have continued our study of -calculus fragments and of their expressivity. We have proven a new congruence result for the pi-calculus: bisimilarity is a congruence in the sub-calculus that does not include restriction nor sum, and features top-level replications only [37] .

Our collaboration with the Focus team in Bologna has been extended with another topic on reversible concurrent models of computation. The notion of reversible computation already has a long history in computer science [54] . Nowadays, it is attracting increasing interest because of its applications in diverse fields, including hardware design, biological modelling, program debugging and testing, and quantum computing. We are interested in investigating whether a reversible programming model can be used as a basis for building dependable, component-based distributed systems. Our initial investigations have focused on extending the higher-order -calculus (HO) ) with reversibility features. We have shown how to derive a reversible form for HO that preserves its structural congruence and we have shown that, surprisingly enough, the obtained reversible HO can be faithfully encoded (up to weak barbed bisimilarity) in HO [38] .