Half-integral Erdős–Pósa conjecture for directed cycles of distinct lengths

From papers

For a digraph DD, a set of directed cycles has distinct lengths when no two of its cycles have the same length. Half-integral distinct-length directed-cycle conjecture. For every k1k\geq1, there exists an integer g(k)g(k) such that every digraph DD contains a set C\mathcal{C} of kk directed cycles of different lengths such that there is no vertex vV(D)v\in V(D) contained in three distinct cycles of C\mathcal{C}, or a set XX of at most g(k)g(k) vertices such that DXD-X contains at most g(k)g(k) different directed cycle lengths. The source leaves this half-integral variant as an open problem after describing a counterexample to the corresponding vertex-disjoint directed-cycle statement.

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Primary source

J. Pascal Gollin, Maximilian Gorsky, Meike Hatzel, Kevin Hendrey, Tony Huynh, Caleb McFarland, Marek Sokołowski, Sebastian Wiederrecht and Paul Wollan, “An Erdős-Pósa theorem for cycles and faces of distinct lengths”, arXiv:2607.06869 (2026).

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