Many calculi exist for modelling various features of object-oriented languages. Many of them are based on -calculus and focus either on statically typed class-based languages or dynamic prototype-based languages.We formalize untyped calculus of decorated objects, informally presented by Bugayenko, which is defined in terms of objects and relies on decoration as a primary mechanism of object extension. It is not based on -calculus, yet with only four basic syntactic constructions is just as complete. We prove the calculus is confluent (i.e. possesses Church-Rosser property), and introduce an abstract machine for call-by-name evaluation. Finally, we provide a sound translation to -calculus with records.

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