arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2007.15822math.CO
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强浸入关系下不含长交替路径的有向图的良拟序

Well-quasi-ordering digraphs with no long alternating paths by the strong immersion relation

Chun-Hung Liu, Irene Muzi

AI总结:

本文针对有向图在强浸入关系下的良拟序问题,证明不含方向改变k次的路径的有向图类(含顶点良拟序标记情形)是良拟序的,且该结果对子图封闭类最优。

摘要:

Nash-Williams的强浸入猜想指出,图在强浸入关系下是良拟序的。也就是说,给定无穷多个图,其中一个图包含另一个图作为其强浸入。本文研究有向图的类似问题。已知有向图在强浸入关系下并非良拟序,但在所有已知的此类无穷反链中,都能找到方向任意多次改变的路径。本文证明其逆命题成立:对每个正整数$k$,不包含方向改变$k$次的路径的有向图类在强浸入关系下是良拟序的,即便顶点由一个良拟序标记也是如此。该结果对子图封闭的有向图类而言是最优的,因为带有顶点标记、方向任意多次改变的路径构成了强浸入关系下的一个无穷反链。

英文摘要:

Nash-Williams' Strong Immersion Conjecture states that graphs are well-quasi-ordered by the strong immersion relation. That is, given infinitely many graphs, one graph contains another graph as a strong immersion. In this paper we study the analogous problem for directed graphs. It is known that digraphs are not well-quasi-ordered by the strong immersion relation, but for all known such infinite antichains, paths that change direction arbitrarily many times can be found. This paper proves that the converse statement is true: for every positive integer $k$, the digraphs that do not contain a path that changes direction $k$ times are well-quasi-ordered by the strong immersion relation, even when vertices are labelled by a well-quasi-order. This result is optimal for classes of digraphs closed under taking subgraphs since paths that change direction arbitrarily many times with vertex-labels form an infinite antichain with respect to the strong immersion relation.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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