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arXiv 1702.06233math.GTmath.CO
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内纽结和4-链有向图

Intrinsically Knotted and 4-Linked Directed Graphs

Thomas Fleming, Joel Foisy

摘要:

我们在有向图的上下文中考虑内在链接和打结。我们构造了一个有向图的例子,它在每个嵌入中都包含一个一致定向的纽结圈。我们还构造了内在3-连通和4-连通有向图的例子。我们引入了两个操作,一致的边收缩和H-循环子收缩,作为特殊情况下的未成年人的有向图,并表明,有一个linkless嵌入的属性是封闭的这些操作。本文分析了无向图$G$和相应的对称有向图$\overline{DG}$中不同结点数和不同链环数之间的关系。最后,我们注意到,一个图,这不是内在联系的最大数量的边缘是$O(n)$在无向的情况下,但$O(n^2)$的有向图。

英文摘要:

We consider intrinsic linking and knotting in the context of directed graphs. We construct an example of a directed graph that contains a consistently oriented knotted cycle in every embedding. We also construct examples of intrinsically 3-linked and 4-linked directed graphs. We introduce two operations, consistent edge contraction and H-cyclic subcontraction, as special cases of minors for digraphs, and show that the property of having a linkless embedding is closed under these operations. We analyze the relationship between the number of distinct knots and links in an undirected graph $G$ and its corresponding symmetric digraph $\overline{DG}$. Finally, we note that the maximum number of edges for a graph that is not intrinsically linked is $O(n)$ in the undirected case, but $O(n^2)$ for directed graphs.

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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