This paper provides a sound foundation for autonomous objects communicating by remote method invocations and futures. As a distributed extension of ς-calculus we define ASP fun , a calculus of functional objects, behaving autonomously and communicating by a request-reply mechanism: requests are method calls handled asynchronously and futures represent awaited results for requests. This results in an object language enabling a concise representation of a set of active objects interacting by

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... hronous method invocations. This paper first presents the ASP fun calculus and its semantics. Then, we provide a type system for ASP fun which guarantees the "progress" property. Most importantly, ASP fun has been formalised; its properties have been formalised and proved using the Isabelle theorem prover and we consider this as an important step in the formalization of distributed languages. This work was also an opportunity to study different binder representations and experiment with two of them in the Isabelle/HOL theorem prover.