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Optimally large cuts in both directions
Abstract
We prove that for every integer d≥2 and all sufficiently large m, every digraph with m edges and minimum outdegree at least d has a vertex bipartition for which each directed cut is of size at least ⌈(d−1)/(2(2d−1))m+d2/(2(2d−1))⌉. The bound is sharp for infinitely many m. This answers for large graphs a question of Scott and proves a conjecture of Lee, Loh, and Sudakov. For d=2 we prove that ⌈ m/6⌉ is achievable for all m. We also establish a stability result characterizing near-extremal graphs.
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BibTeX
@misc{folz2026optimally,
title = {{Optimally large cuts in both directions}},
author = {Frederic Folz and Mykhaylo Tyomkyn},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.21381},
eprint = {2610.21381},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.21381},
}
RIS
TY - UNPB
TI - Optimally large cuts in both directions
AU - Frederic Folz
AU - Mykhaylo Tyomkyn
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.21381
UR - https://arxiv.org/abs/2610.21381
AB - We prove that for every integer d≥2 and all sufficiently large m, every digraph with m edges and minimum outdegree at least d has a vertex bipartition for which each directed cut is of size at least ⌈(d−1)/(2(2d−1))m+d^2/(2(2d−1))⌉. The bound is sharp for infinitely many m. This answers for large graphs a question of Scott and proves a conjecture of Lee, Loh, and Sudakov. For d=2 we prove that ⌈ m/6⌉ is achievable for all m. We also establish a stability result characterizing near-extremal graphs.
ER -