Recent work has shown that presheaf categories provide a general model of concurrency, with an inbuilt notion of bisimulation based on open maps. Here it is shown how this approach can also han- die systems where the language of actions may change dynamically as a process evolves. The example is the -/r-calculus, a calculus for 'mobile processes' whose communication topology varies as channels are created and discarded. A denotational semantics is described for the 7r-calculus within an indexed category of profunctors; the model is fully abstract for bisimilarity, in the sense that bisimulation in the model, obtained from open maps, coincides with the usual bisimulation obtained from the op- erational semantics of the 7r-calculus. While attention is concentrated on the 'late' semantics of the 7r-calculus, it is indicated how the 'early' and other variants can also be captured.
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