Lucas Aragão , João Pedro Marciano , Walner Mendonça
{"title":"拉姆齐良好路径的程度条件","authors":"Lucas Aragão , João Pedro Marciano , Walner Mendonça","doi":"10.1016/j.ejc.2024.104082","DOIUrl":null,"url":null,"abstract":"<div><div>A classical result of Chvátal implies that if <span><math><mrow><mi>n</mi><mo>≥</mo><mrow><mo>(</mo><mi>r</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mrow><mo>(</mo><mi>t</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mo>+</mo><mn>1</mn></mrow></math></span>, then any colouring of the edges of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> in red and blue contains either a monochromatic red <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>r</mi></mrow></msub></math></span> or a monochromatic blue <span><math><msub><mrow><mi>P</mi></mrow><mrow><mi>t</mi></mrow></msub></math></span>. We study a natural generalisation of his result, determining the exact minimum degree condition for a graph <span><math><mi>G</mi></math></span> on <span><math><mrow><mi>n</mi><mo>=</mo><mrow><mo>(</mo><mi>r</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mrow><mo>(</mo><mi>t</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mo>+</mo><mn>1</mn></mrow></math></span> vertices which guarantees that the same Ramsey property holds in <span><math><mi>G</mi></math></span>. In particular, using a slight generalisation of a result of Haxell, we show that <span><math><mrow><mi>δ</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>≥</mo><mi>n</mi><mo>−</mo><mfenced><mrow><mi>t</mi><mo>/</mo><mn>2</mn></mrow></mfenced></mrow></math></span> suffices, and that this bound is best possible. We also use a classical result of Bollobás, Erdős, and Straus to prove a tight minimum degree condition in the case <span><math><mrow><mi>r</mi><mo>=</mo><mn>3</mn></mrow></math></span> for all <span><math><mrow><mi>n</mi><mo>≥</mo><mn>2</mn><mi>t</mi><mo>−</mo><mn>1</mn></mrow></math></span>.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":null,"pages":null},"PeriodicalIF":1.0000,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Degree conditions for Ramsey goodness of paths\",\"authors\":\"Lucas Aragão , João Pedro Marciano , Walner Mendonça\",\"doi\":\"10.1016/j.ejc.2024.104082\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>A classical result of Chvátal implies that if <span><math><mrow><mi>n</mi><mo>≥</mo><mrow><mo>(</mo><mi>r</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mrow><mo>(</mo><mi>t</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mo>+</mo><mn>1</mn></mrow></math></span>, then any colouring of the edges of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> in red and blue contains either a monochromatic red <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>r</mi></mrow></msub></math></span> or a monochromatic blue <span><math><msub><mrow><mi>P</mi></mrow><mrow><mi>t</mi></mrow></msub></math></span>. We study a natural generalisation of his result, determining the exact minimum degree condition for a graph <span><math><mi>G</mi></math></span> on <span><math><mrow><mi>n</mi><mo>=</mo><mrow><mo>(</mo><mi>r</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mrow><mo>(</mo><mi>t</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mo>+</mo><mn>1</mn></mrow></math></span> vertices which guarantees that the same Ramsey property holds in <span><math><mi>G</mi></math></span>. In particular, using a slight generalisation of a result of Haxell, we show that <span><math><mrow><mi>δ</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>≥</mo><mi>n</mi><mo>−</mo><mfenced><mrow><mi>t</mi><mo>/</mo><mn>2</mn></mrow></mfenced></mrow></math></span> suffices, and that this bound is best possible. We also use a classical result of Bollobás, Erdős, and Straus to prove a tight minimum degree condition in the case <span><math><mrow><mi>r</mi><mo>=</mo><mn>3</mn></mrow></math></span> for all <span><math><mrow><mi>n</mi><mo>≥</mo><mn>2</mn><mi>t</mi><mo>−</mo><mn>1</mn></mrow></math></span>.</div></div>\",\"PeriodicalId\":50490,\"journal\":{\"name\":\"European Journal of Combinatorics\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":1.0000,\"publicationDate\":\"2024-10-18\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"European Journal of Combinatorics\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0195669824001677\",\"RegionNum\":3,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"European Journal of Combinatorics","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0195669824001677","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATHEMATICS","Score":null,"Total":0}
A classical result of Chvátal implies that if , then any colouring of the edges of in red and blue contains either a monochromatic red or a monochromatic blue . We study a natural generalisation of his result, determining the exact minimum degree condition for a graph on vertices which guarantees that the same Ramsey property holds in . In particular, using a slight generalisation of a result of Haxell, we show that suffices, and that this bound is best possible. We also use a classical result of Bollobás, Erdős, and Straus to prove a tight minimum degree condition in the case for all .
期刊介绍:
The European Journal of Combinatorics is a high standard, international, bimonthly journal of pure mathematics, specializing in theories arising from combinatorial problems. The journal is primarily open to papers dealing with mathematical structures within combinatorics and/or establishing direct links between combinatorics and other branches of mathematics and the theories of computing. The journal includes full-length research papers on important topics.