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arXiv · 2611.00720

Sharp digirth bounds for C(k,k)-subdivisions in digraphs

Hao Zhang·Panpan Cheng·Jin Yan·Tong Zhou
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Abstract

For an integer $k\ge2$, let $C(k,k)$ denote the oriented cycle formed by two internally vertex-disjoint directed paths of length $k$ with the same initial and terminal vertices. We extend a problem of Picasarri-Arrieta and Rambaud [European J. Combin. 122 (2024)] on subdivisions of $C(k,k)$ to digraphs with several vertices of out-degree one. Following the sharp result of Chen et al. [arXiv:2610.38574v1 (2026)] for at most one such vertex, we determine the exact digirth threshold when at most $r\ge4$ such vertices are permitted. Specifically, for all integers $k\ge2$ and $r\ge4$, every digraph of minimum out-degree at least one, with at most $r$ vertices of out-degree one and digirth at least $r(k-1)+1$, contains a subdivision of $C(k,k)$.

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Hao Zhang, Panpan Cheng, Jin Yan, Tong Zhou. 2026-10-31. Sharp digirth bounds for C(k,k)-subdivisions in digraphs. https://arxiv.org/abs/2611.00720

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