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In mathematics, the Erdős–Burr conjecture is a problem concerning the Ramsey number of sparse graphs. The conjecture is named after Paul Erdős and Stefan Burr, and is one of many conjectures named after Erdős; it states that the Ramsey number of graphs in any sparse family of graphs should grow linearly in the number of vertices of the graph. In 2015, a proof of the conjecture was announced by Choongbum Lee.〔; 〕 ==Definitions== If ''G'' is an undirected graph, then the degeneracy of ''G'' is the minimum number ''p'' such that every subgraph of ''G'' contains a vertex of degree ''p'' or smaller. A graph with degeneracy ''p'' is called ''p''-degenerate. Equivalently, a ''p''-degenerate graph is a graph that can be reduced to the empty graph by repeatedly removing a vertex of degree ''p'' or smaller. It follows from Ramsey's theorem that for any graph ''G'' there exists a least integer , the ''Ramsey number'' of ''G'', such that any complete graph on at least vertices whose edges are coloured red or blue contains a monochromatic copy of ''G''. For instance, the Ramsey number of a triangle is 6: no matter how the edges of a complete graph on six vertices are colored red or blue, there is always either a red triangle or a blue triangle. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Erdős–Burr conjecture」の詳細全文を読む スポンサード リンク
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