The concept of extension-based proofs models the idea of a valency argument, which is widely used in distributed computing. Extension-based proofs are limited in power: it has been shown that there is no extension-based proof of the impossibility of a wait-free protocol for (n,k)-set agreement among n > k ≥ 2 processes. There are only a few tasks that have been proven to have no extension-based proof of the impossibility, since the techniques in these works are closely related to the specific task. We give a necessary and sufficient condition for colorless tasks to have no extension-based proofs of the impossibility of wait-free protocols in the NIIS model. We introduce a general adversarial strategy decoupled from any concrete task specification. In this strategy, some properties of the chromatic subdivision that is widely used in distributed computing are proved.
@InProceedings{shi_et_al:LIPIcs.DISC.2024.54, author = {Shi, Yusong and Liu, Weidong}, title = {{Brief Announcement: Colorless Tasks and Extension-Based Proofs}}, booktitle = {38th International Symposium on Distributed Computing (DISC 2024)}, pages = {54:1--54:6}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-352-2}, ISSN = {1868-8969}, year = {2024}, volume = {319}, editor = {Alistarh, Dan}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.54}, URN = {urn:nbn:de:0030-drops-212821}, doi = {10.4230/LIPIcs.DISC.2024.54}, annote = {Keywords: Colorless tasks, Impossibility proofs, Extension-based proof} }
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