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Software's expense owes partly to frequent reimplementation of similar functionality and partly to maintenance of patches, ports or components targeting evolving interfaces. More modular non-invasive approaches are unpopular because they entail laborious wrapper code. We propose Cake, a rule-based language describing compositions using interface relations. To evaluate it, we compare several existing wrappers with reimplemented Cake versions, finding the latter to be simpler and better modularised.