Weakly linked embeddings of pairs of complete graphs in $\mathbb{R}^3$

Fuente: arXiv
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Main Authors: Di, James, Flapan, Erica, Johnson, Spencer, Thompson, Daniel, Tuffley, Christopher
Format: Preprint
Published: 2020
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author Di, James
Flapan, Erica
Johnson, Spencer
Thompson, Daniel
Tuffley, Christopher
author_facet Di, James
Flapan, Erica
Johnson, Spencer
Thompson, Daniel
Tuffley, Christopher
contents Let $G$ and $H$ be disjoint embeddings of complete graphs $K_m$ and $K_n$ in $\mathbb{R}^3$ such that some cycle in $G$ links a cycle in $H$ with non-zero linking number. We say that $G$ and $H$ are *weakly linked* if the absolute value of the linking number of any cycle in $G$ with a cycle in $H$ is $0$ or $1$. Our main result is an algebraic characterisation of when a pair of disjointly embedded complete graphs is weakly linked. As a step towards this result, we show that if $G$ and $H$ are weakly linked, then each contains either a vertex common to all triangles linking the other or a triangle which shares an edge with all triangles linking the other. All families of weakly linked pairs of complete graphs are then characterised by which of these two cases holds in each complete graph.
format Preprint
id arxiv_https___arxiv_org_abs_2012_11030
institution arXiv
publishDate 2020
record_format arxiv
spellingShingle Weakly linked embeddings of pairs of complete graphs in $\mathbb{R}^3$
Di, James
Flapan, Erica
Johnson, Spencer
Thompson, Daniel
Tuffley, Christopher
Geometric Topology
57M15, 57K10
Let $G$ and $H$ be disjoint embeddings of complete graphs $K_m$ and $K_n$ in $\mathbb{R}^3$ such that some cycle in $G$ links a cycle in $H$ with non-zero linking number. We say that $G$ and $H$ are *weakly linked* if the absolute value of the linking number of any cycle in $G$ with a cycle in $H$ is $0$ or $1$. Our main result is an algebraic characterisation of when a pair of disjointly embedded complete graphs is weakly linked. As a step towards this result, we show that if $G$ and $H$ are weakly linked, then each contains either a vertex common to all triangles linking the other or a triangle which shares an edge with all triangles linking the other. All families of weakly linked pairs of complete graphs are then characterised by which of these two cases holds in each complete graph.
title Weakly linked embeddings of pairs of complete graphs in $\mathbb{R}^3$
topic Geometric Topology
57M15, 57K10
url https://arxiv.org/abs/2012.11030