An upper bound for a ramsey type problem for k-connected subgraphs

For any positive integer k , let r 2 ( k ) denote the smallest integer n such that every 2-edge-colored complete graph K n contains a monochromatic k -connected subgraph. Matula established the bound 4 ( k - 1 ) + 1 ≤ r 2 ( k ) < ( 3 + 11 / 3 ) ( k - 1 ) + 1 . It is known that r 2 ( k ) = 4 ( k -...

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Published in:Graphs and combinatorics Vol. 41; no. 6; p. 128
Main Authors: Chen, Murong, Xie, Qiqin
Format: Journal Article
Language:English
Published: Tokyo Springer Japan 01.12.2025
Springer Nature B.V
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ISSN:0911-0119, 1435-5914
Online Access:Get full text
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Summary:For any positive integer k , let r 2 ( k ) denote the smallest integer n such that every 2-edge-colored complete graph K n contains a monochromatic k -connected subgraph. Matula established the bound 4 ( k - 1 ) + 1 ≤ r 2 ( k ) < ( 3 + 11 / 3 ) ( k - 1 ) + 1 . It is known that r 2 ( k ) = 4 ( k - 1 ) + 1 f o r k = 1 , 2 (by Bollobás and Gyárfás) and for k = 3 (by Liu, Morris, and Prince). We prove that for k ≥ 2 and n > ( 3 + 497 - 1 16 ) ( k - 1 ) , every 2-edge-colored K n contains a monochromatic k -connected subgraph with at least 2 ( k - 1 ) vertices. This result improves the upper bound of r 2 ( k ) to ⌈ ( 3 + 497 - 1 16 ) ( k - 1 ) ⌉ for all k ≥ 4 .
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ISSN:0911-0119
1435-5914
DOI:10.1007/s00373-025-02993-8