The issue of this work is how to type mobility, in the sense that we tackle the problem of typing not only mobile agents but also their movement. This yields higher-order types for agents. To that end we first provide a new definition of the Seal Calculus that gets rid of existing inessential features while preserving the distinctive characteristics of the Seal model. Then we discuss the use of interfaces to type agents and define the type system. The interpretation induced by this type system

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... s that interfaces describe interaction effects rather than, as it is customary, provided services. We discuss at length the difference of the two interpretations and justify our choice of the former.