Counterexamples to Two Conjectures on Tangles in Matroid Minors

Zhen Chen; Zhuo Li

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arXiv · 2610.23059

Counterexamples to Two Conjectures on Tangles in Matroid Minors

Zhen Chen·Zhuo Li

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Abstract

We give counterexamples to two conjectures of Brettell, Jowett, Oxley, Semple, and Whittle concerning tangles in matroid minors. We construct a matroid $P_0$ with a tangle $\mathcal T$ of order seven. For each $i\in\{4,5,6,7\}$, let $\mathcal T_i$ denote its order-$i$ truncation. No proper minor $N$ of $P_0$ admits, for every such $i$, a tangle of order $i$ whose breadth equals that of $\mathcal T_i$, and $P_0$ is not weakly $4$-connected. We also construct a matroid $P_1$ with a tangle of order four and breadth six, but no internally $4$-connected minor of $P_1$ admits a tangle of order four.

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Zhen Chen, Zhuo Li. 2026-10-16. Counterexamples to Two Conjectures on Tangles in Matroid Minors. https://arxiv.org/abs/2610.23059

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