By adding re exion to the chemical machine of Berry and Boudol, we obtain a formal model of concurrency that is consistent with mobility and distribution. Our model provides the foundations of a programming language with functional and object-oriented features. It can also be seen as a process calculus, the join-calculus, which we prove equivalent to the -calculus of Milner, Parrow and Walker. * ) 'readyhlaseri j jobh1i jobh2i Denoted D or J . P , a reaction consumes compound molecules that

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... a speci c join pattern J, and produces new molecules in the solution that are copies of P where the formal parameters of J have been instantiated to the transmitted values. This corresponds to reduction steps on the whole solution (R M ) ;! (R M 0 ). Continuing our example, we add a reaction that matches printers and jobs, then sends the lename to the printer: