Characterizing consensus in the Heard-Of model
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The Heard-Of model is a simple and relatively expressive model of distributed computation. Because of this, it has gained a considerable attention of the verification community. We give a characterization of all algorithms solving consensus in a fragment of this model. The fragment is big enough to cover many prominent consensus algorithms. The characterization is purely syntactic: it is expressed in terms of some conditions on the text of the algorithm. One of the recent methods of verification of distributed algorithms is to abstract an algorithm to the Heard-Of model and then to verify the abstract algorithm using semi-automatic procedures. Our results allow, in some cases, to avoid the second step in this methodology.
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