  Proving correctness of distributed or concurrent algorithms is a
mind-challenging and complex process. Slight errors in the reasoning are
difficult to find, calling for computer-checked proof systems. In order to
build computer-checked proofs with usual tools, such as Coq or TLA+, having
sequential specifications of all base objects that are used as building blocks
in a given algorithm is a requisite to provide a modular proof built by
composition. Alas, many concurrent objects do not have a sequential
specification. This article describes a systematic method to transform any
task, a specification method that captures concurrent one-shot distributed
problems, into a sequential specification involving two calls, Set and Get.
This transformation allows system designers to compose proofs, thus providing a
framework for modular computer-checked proofs of algorithms designed using
tasks and sequential objects as building blocks. The Moir&Anderson
implementation of renaming using splitters is an iconic example of such
algorithms designed by composition.
