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arXiv · 2609.39656

Testing Induced-Subgraph Freeness in Outerplanar Graphs under the Random-Neighbor Oracle

Pan Peng·Kefan Yu
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Abstract

We prove that, for every fixed nonempty graph $H$, induced-$H$-freeness is testable with $\varepsilon^{-O_H(1)}$ queries on outerplanar graphs with no maximum-degree bound in the $\textit{random-neighbor model}$, where each query at a vertex returns a uniformly random neighbor. Thus, the query complexity is polynomial in $1/\varepsilon$ and independent of the number $n$ of vertices. Previously, the best bound known for this problem was the $\operatorname{poly}(\log n)$-query guarantee that follows from the general outerplanar-graph tester of Babu, Khoury, and Newman (2016) in the stronger $\textit{adjacency-list model}$, which provides exact degree queries and indexed access to neighbors. Our tester has $\textit{two-sided error}$, which is necessary in general: induced-$P_3$-freeness has no one-sided constant-query tester in the random-neighbor model, even on outerplanar graphs of maximum degree two.

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Pan Peng, Kefan Yu. 2026-09-30. Testing Induced-Subgraph Freeness in Outerplanar Graphs under the Random-Neighbor Oracle. https://arxiv.org/abs/2609.39656

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