
arXiv: 2011.14074
For fixed finite graphs $G$, $H$, a common problem in Ramsey theory is to study graphs $F$ such that $F \to (G,H)$, i.e. every red-blue coloring of the edges of $F$ produces either a red $G$ or a blue $H$. We generalize this study to infinite graphs $G$, $H$; in particular, we want to determine if there is a minimal such $F$. This problem has strong connections to the study of self-embeddable graphs: infinite graphs which properly contain a copy of themselves. We prove some compactness results relating this problem to the finite case, then give some general conditions for a pair $(G,H)$ to have a Ramsey-minimal graph. We use these to prove, for example, that if $G=S_\infty$ is an infinite star and $H=nK_2$, $n \geqslant 1$ is a matching, then the pair $(S_\infty,nK_2)$ admits no Ramsey-minimal graphs.
Extremal problems in graph theory, matching, Ramsey theory, Generalized Ramsey theory, Mathematics - Logic, Infinite graphs, comb graph, Isomorphism problems in graph theory (reconstruction conjecture, etc.) and homomorphisms (subgraph embedding, etc.), FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Koenig's Lemma, Logic (math.LO), 05C55, 05D10, 05C63, 05C60, self-embeddable graph
Extremal problems in graph theory, matching, Ramsey theory, Generalized Ramsey theory, Mathematics - Logic, Infinite graphs, comb graph, Isomorphism problems in graph theory (reconstruction conjecture, etc.) and homomorphisms (subgraph embedding, etc.), FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Koenig's Lemma, Logic (math.LO), 05C55, 05D10, 05C63, 05C60, self-embeddable graph
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