Yan Cao, Guantao Chen, Guangming Jing, Songling Shan
{"title":"Overfullness of edge-critical graphs with small minimal core degree","authors":"Yan Cao, Guantao Chen, Guangming Jing, Songling Shan","doi":"10.1002/jgt.23069","DOIUrl":null,"url":null,"abstract":"<p>Let <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> be a simple graph. Let <math>\n <semantics>\n <mrow>\n <mi>Δ</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n <annotation> ${\\rm{\\Delta }}(G)$</annotation>\n </semantics></math> and <math>\n <semantics>\n <mrow>\n <mi>χ</mi>\n \n <mo>′</mo>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n <annotation> $\\chi ^{\\prime} (G)$</annotation>\n </semantics></math> be the maximum degree and the chromatic index of <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math>, respectively. We call <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> <i>overfull</i> if <math>\n <semantics>\n <mrow>\n <mo>∣</mo>\n \n <mi>E</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo>∣</mo>\n \n <mo>∕</mo>\n \n <mrow>\n <mo>⌊</mo>\n \n <mrow>\n <mo>∣</mo>\n \n <mi>V</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo>∣</mo>\n \n <mo>∕</mo>\n \n <mn>2</mn>\n </mrow>\n \n <mo>⌋</mo>\n </mrow>\n \n <mo>></mo>\n \n <mi>Δ</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n <annotation> $| E(G)| \\unicode{x02215}\\lfloor | V(G)| \\unicode{x02215}2\\rfloor \\gt {\\rm{\\Delta }}(G)$</annotation>\n </semantics></math>, and <i>critical</i> if <math>\n <semantics>\n <mrow>\n <mi>χ</mi>\n \n <mo>′</mo>\n \n <mrow>\n <mo>(</mo>\n \n <mi>H</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo><</mo>\n \n <mi>χ</mi>\n \n <mo>′</mo>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n <annotation> $\\chi ^{\\prime} (H)\\lt \\chi ^{\\prime} (G)$</annotation>\n </semantics></math> for every proper subgraph <math>\n <semantics>\n <mrow>\n <mi>H</mi>\n </mrow>\n <annotation> $H$</annotation>\n </semantics></math> of <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math>. Clearly, if <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> is overfull then <math>\n <semantics>\n <mrow>\n <mi>χ</mi>\n \n <mo>′</mo>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo>=</mo>\n \n <mi>Δ</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n <annotation> $\\chi ^{\\prime} (G)={\\rm{\\Delta }}(G)+1$</annotation>\n </semantics></math>. The <i>core</i> of <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math>, denoted by <math>\n <semantics>\n <mrow>\n <msub>\n <mi>G</mi>\n \n <mi>Δ</mi>\n </msub>\n </mrow>\n <annotation> ${G}_{{\\rm{\\Delta }}}$</annotation>\n </semantics></math>, is the subgraph of <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> induced by all its maximum degree vertices. We believe that utilizing the core degree condition could be considered as an approach to attack the overfull conjecture. Along this direction, we in this paper show that for any integer <math>\n <semantics>\n <mrow>\n <mi>k</mi>\n \n <mo>≥</mo>\n \n <mn>2</mn>\n </mrow>\n <annotation> $k\\ge 2$</annotation>\n </semantics></math>, if <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> is critical with <math>\n <semantics>\n <mrow>\n <mi>Δ</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo>≥</mo>\n \n <mfrac>\n <mn>2</mn>\n \n <mn>3</mn>\n </mfrac>\n \n <mi>n</mi>\n \n <mo>+</mo>\n \n <mfrac>\n <mrow>\n <mn>3</mn>\n \n <mi>k</mi>\n </mrow>\n \n <mn>2</mn>\n </mfrac>\n </mrow>\n <annotation> ${\\rm{\\Delta }}(G)\\ge \\frac{2}{3}n+\\frac{3k}{2}$</annotation>\n </semantics></math> and <math>\n <semantics>\n <mrow>\n <mi>δ</mi>\n \n <mrow>\n <mo>(</mo>\n \n <msub>\n <mi>G</mi>\n \n <mi>Δ</mi>\n </msub>\n \n <mo>)</mo>\n </mrow>\n \n <mo>≤</mo>\n \n <mi>k</mi>\n </mrow>\n <annotation> $\\delta ({G}_{{\\rm{\\Delta }}})\\le k$</annotation>\n </semantics></math>, then <math>\n <semantics>\n <mrow>\n <mi>G</mi>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> is overfull.</p>","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":null,"pages":null},"PeriodicalIF":0.9000,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Graph Theory","FirstCategoryId":"100","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23069","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0
Abstract
Let be a simple graph. Let and be the maximum degree and the chromatic index of , respectively. We call overfull if , and critical if for every proper subgraph of . Clearly, if is overfull then . The core of , denoted by , is the subgraph of induced by all its maximum degree vertices. We believe that utilizing the core degree condition could be considered as an approach to attack the overfull conjecture. Along this direction, we in this paper show that for any integer , if is critical with and , then is overfull.
期刊介绍:
The Journal of Graph Theory is devoted to a variety of topics in graph theory, such as structural results about graphs, graph algorithms with theoretical emphasis, and discrete optimization on graphs. The scope of the journal also includes related areas in combinatorics and the interaction of graph theory with other mathematical sciences.
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