A definition of minor (in graph theory)

Many people I talk to about graph theory feel some uneasiness when it comes to the notion of “minor”. I want to try to alleviate this feeling by providing the definiton of minor that I work with.

First an easy definition. If G is a simple, undirected graph and S, T\subseteq V(G) are non-empty and disjoint, we say that S, T are connected to each other if there are s\in S, t\in T such that \{s,t\}\in E(G).

Let G, H be simple, undirected graphs. We say that G is a minor of H if there is a collection {\cal S} of non-empty, mutually disjoint, and connected subsets of V(H) and a bijection \varphi:V(G) \to {\cal S} such that

whenever v,w\in V(G) and \{v,w\}\in E(G) then the sets \varphi(v) and \varphi(w) are connected to each other in H.


About dominiczypen

I'm interested in general topology, order theory, and graph theory. This link takes you to my preprints on arXiv.
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