Orientation Does Not Help with 3-Coloring a Grid in Online-LOCAL

The online-LOCAL and SLOCAL models are extensions of the LOCAL model where nodes are processed in a sequential but potentially adversarial order. So far, the only problem we know of where the global memory of the online-LOCAL model has an advantage over SLOCAL is 3-coloring bipartite graphs. Recently, Chang et al. [PODC 2024] showed that even in grids, 3-coloring requires Ω(log n) locality in deterministic online-LOCAL. This result was subsequently extended by Akbari et al. [STOC 2025] to also hold in randomized online-LOCAL. However, both proofs heavily rely on the assumption that the algorithm does not have access to the orientation of the underlying grid. In this paper, we show how to lift this requirement and obtain the same lower bound (against either model) even when the algorithm is explicitly given a globally consistent orientation of the grid.

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Publication Details

Journal
Aaltodoc (Aalto University)
Published
2026-01-01
DOI
https://doi.org/10.4230/lipics.opodis.2025.19
Primary Topic
Complexity and Algorithms in Graphs
Type
article
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article

Orientation Does Not Help with 3-Coloring a Grid in Online-LOCAL

Henrik Lievonen, Avinandan Das, Massimo Equi, Augusto Modanese et al.
Aaltodoc (Aalto University)
Complexity and Algorithms in Graphs
article

Orientation Does Not Help with 3-Coloring a Grid in Online-LOCAL

Henrik Lievonen, Avinandan Das, Massimo Equi, Augusto Modanese, Thomas Boudier, Ronja Stimpert, Filippo Casagrande
article en

Abstract

The online-LOCAL and SLOCAL models are extensions of the LOCAL model where nodes are processed in a sequential but potentially adversarial order. So far, the only problem we know of where the global memory of the online-LOCAL model has an advantage over SLOCAL is 3-coloring bipartite graphs. Recently, Chang et al. [PODC 2024] showed that even in grids, 3-coloring requires Ω(log n) locality in deterministic online-LOCAL. This result was subsequently extended by Akbari et al. [STOC 2025] to also hold in randomized online-LOCAL. However, both proofs heavily rely on the assumption that the algorithm does not have access to the orientation of the underlying grid. In this paper, we show how to lift this requirement and obtain the same lower bound (against either model) even when the algorithm is explicitly given a globally consistent orientation of the grid.

Aaltodoc (Aalto University)
Gran Sasso Science Institute (IT), Aalto University (FI)
Openalex Percentile: Top 93%
Complexity and Algorithms in Graphs
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