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In this work, we give a complete topological characterisation of the $t$-resilient solvability of approximate agreement on graphs and simplicial complexes in asynchronous shared-memory systems with read-write registers. As a result, we answer several open problems related to different variants of approximate agreement on graphs. For example, we give the first proof of Ledent's conjecture [PODC 2021] about the wait-free solvability of clique agreement.
In fact, we show a more general result: clique agreement is $t$-resilient solvable on a graph $G$ if and only if its clique complex is $(t-1)$-connected in the homotopical sense. We also show that clique and monophonic agreement are solvable on the same class of graphs, but there exists a separation between monophonic and geodesic agreement, answering a question by Alistarh et al. [TCS 2023]. In the message-passing setting, our results imply new resilience bounds for asynchronous approximate agreement and round lower bounds for synchronous approximate agreement on graphs.
From: Joel Rybicki [view email]
[v1]
Tue, 23 Jun 2026 14:56:31 UTC (370 KB)
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