{"title":"Removable edges in near-bipartite bricks","authors":"Yipei Zhang, Fuliang Lu, Xiumei Wang, Jinjiang Yuan","doi":"10.1002/jgt.23173","DOIUrl":null,"url":null,"abstract":"<p>An edge <span></span><math>\n \n <mrow>\n <mi>e</mi>\n </mrow></math> of a matching covered graph <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> is <i>removable</i> if <span></span><math>\n \n <mrow>\n <mi>G</mi>\n \n <mo>−</mo>\n \n <mi>e</mi>\n </mrow></math> is also matching covered. The notion of removable edge arises in connection with ear decompositions of matching covered graphs introduced by Lovász and Plummer. A nonbipartite matching covered graph <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> is a <i>brick</i> if it is free of nontrivial tight cuts. Carvalho, Lucchesi and Murty proved that every brick other than <span></span><math>\n \n <mrow>\n <msub>\n <mi>K</mi>\n \n <mn>4</mn>\n </msub>\n </mrow></math> and <span></span><math>\n \n <mrow>\n <mover>\n <msub>\n <mi>C</mi>\n \n <mn>6</mn>\n </msub>\n \n <mo>¯</mo>\n </mover>\n </mrow></math> has at least <span></span><math>\n \n <mrow>\n <mi>Δ</mi>\n \n <mo>−</mo>\n \n <mn>2</mn>\n </mrow></math> removable edges. A brick <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> is <i>near-bipartite</i> if it has a pair of edges <span></span><math>\n \n <mrow>\n <mrow>\n <mo>{</mo>\n \n <mrow>\n <msub>\n <mi>e</mi>\n \n <mn>1</mn>\n </msub>\n \n <mo>,</mo>\n \n <msub>\n <mi>e</mi>\n \n <mn>2</mn>\n </msub>\n </mrow>\n \n <mo>}</mo>\n </mrow>\n </mrow></math> such that <span></span><math>\n \n <mrow>\n <mi>G</mi>\n \n <mo>−</mo>\n \n <mrow>\n <mo>{</mo>\n \n <mrow>\n <msub>\n <mi>e</mi>\n \n <mn>1</mn>\n </msub>\n \n <mo>,</mo>\n \n <msub>\n <mi>e</mi>\n \n <mn>2</mn>\n </msub>\n </mrow>\n \n <mo>}</mo>\n </mrow>\n </mrow></math> is a bipartite matching covered graph. In this paper, we show that in a near-bipartite brick <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> with at least six vertices, every vertex of <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math>, except at most six vertices of degree three contained in two disjoint triangles, is incident with at most two nonremovable edges; consequently, <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> has at least <span></span><math>\n \n <mrow>\n <mfrac>\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>6</mn>\n </mrow>\n \n <mn>2</mn>\n </mfrac>\n </mrow></math> removable edges. Moreover, all graphs attaining this lower bound are characterized.</p>","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"108 1","pages":"113-135"},"PeriodicalIF":0.9000,"publicationDate":"2024-09-09","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.23173","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
An edge of a matching covered graph is removable if is also matching covered. The notion of removable edge arises in connection with ear decompositions of matching covered graphs introduced by Lovász and Plummer. A nonbipartite matching covered graph is a brick if it is free of nontrivial tight cuts. Carvalho, Lucchesi and Murty proved that every brick other than and has at least removable edges. A brick is near-bipartite if it has a pair of edges such that is a bipartite matching covered graph. In this paper, we show that in a near-bipartite brick with at least six vertices, every vertex of , except at most six vertices of degree three contained in two disjoint triangles, is incident with at most two nonremovable edges; consequently, has at least removable edges. Moreover, all graphs attaining this lower bound are characterized.
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.
A subscription to the Journal of Graph Theory includes a subscription to the Journal of Combinatorial Designs .