,
Antonio Fernández Anta
,
Chryssis Georgiou
,
Nicolas Nicolaou
,
Junlang Wang
Creative Commons Attribution 4.0 International license
This paper explores necessary and sufficient system conditions to solve distributed tasks with binary outputs (i.e., tasks with output values in {0,1}). We focus on the distinct output sets of values a task can produce (intentionally disregarding validity and value multiplicity), considering that some processes may output no value. In a distributed system with n processes, of which up to t ≤ n can crash, we provide a complete characterization of the tight conditions on n and t under which every class of tasks with binary outputs is solvable, for both synchronous and asynchronous systems. This output-set approach yields highly general results: it unifies multiple distributed computing problems, such as binary consensus and symmetry breaking, and it produces impossibility proofs that hold for stronger task formulations, including those that consider validity, account for value multiplicity, or move beyond binary outputs.
@InProceedings{albouy_et_al:LIPIcs.OPODIS.2025.5,
author = {Albouy, Timoth\'{e} and Fern\'{a}ndez Anta, Antonio and Georgiou, Chryssis and Nicolaou, Nicolas and Wang, Junlang},
title = {{Tight Conditions for Binary-Output Tasks Under Crashes}},
booktitle = {29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
pages = {5:1--5:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-409-3},
ISSN = {1868-8969},
year = {2026},
volume = {361},
editor = {Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.5},
URN = {urn:nbn:de:0030-drops-251786},
doi = {10.4230/LIPIcs.OPODIS.2025.5},
annote = {Keywords: Distributed solvability, Asynchrony, Synchrony, Impossibility proofs, Binary-output tasks, Crash tolerance, Disagreement}
}