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Combinatorial properties of infinite sets. This is a corner-point of set theory and combinatorics.
4
votes
1
answer
367
views
When is it true that if $G$ is isomorphic to a spanning subgraph of $H$ and vice versa, then...
When is it true that if $G$ is isomorphic to a spanning subgraph of $H$ and $H$ is isomorphic to a spanning subgraph of $G$, then $G$ is isomorphic to $H$?
Clearly this is true if $G$ and $H$ are fini …
2
votes
Accepted
Injective choice function for infinite complete linear hypergraphs
After the discussion above, here is what I think is the cleanest proof and it has the property that $f$ is bijection (unless there is an edge of order 1).
If there is an edge of order 1, then we must …
1
vote
Graph $G$ such that removing an edge leaves $G$ "unchanged"
How about a graph $G=(V,E)$ consisting of infinitely many isolated vertices and infinitely many disjoint edges. Like the random graph it has the property that for all $e\in E$, $G\simeq (V, E\setminu …
3
votes
Induced subgraphs of the almost-disjointness graph
My first thought for the case where $|V|\leq \aleph_0$ is that surely the Rado graph can be constructed as an induced subgraph of $([\omega]^{\omega}, E)$ (since the Rado graph contains a copy of ever …
3
votes
1
answer
292
views
Perfect matchings in infinite regular bipartite graphs
This question was motivated by a discussion here and is related to a previous question here.
Let $\kappa$ and $\lambda$ be cardinals such that $0<\lambda\leq \kappa$. Let $G=(A\cup B, E)$ be a bipart …
4
votes
Accepted
Is König's Property for graphs inheritable from finite subgraphs?
(Just making my comment an answer as suggested.)
If every finite subgraph of $G$ satisfies Kőnig's Property, then $G$ has no odd cycles and is thus bipartite. Aharoni
(König's Duality Theorem For Infi …