{"title":"无P_5$和无爪图中最长路径的非空交集","authors":"Paloma T. Lima, Amir Nikabadi","doi":"arxiv-2409.07366","DOIUrl":null,"url":null,"abstract":"A family $\\mathcal{F}$ of graphs is a \\textit{Gallai family} if for every\nconnected graph $G\\in \\mathcal{F}$, all longest paths in $G$ have a common\nvertex. While it is not known whether $P_5$-free graphs are a Gallai family,\nLong Jr., Milans, and Munaro [The Electronic Journal of Combinatorics, 2023]\nshowed that this is \\emph{not} the case for the class of claw-free graphs. We\ngive a complete characterization of the graphs $H$ of size at most five for\nwhich $(\\text{claw}, H)$-free graphs form a Gallai family. We also show that\n$(P_5, H)$-free graphs form a Gallai family if $H$ is a triangle, a paw, or a\ndiamond. Both of our results are constructive.","PeriodicalId":501407,"journal":{"name":"arXiv - MATH - Combinatorics","volume":"45 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Non-empty intersection of longest paths in $P_5$-free and claw-free graphs\",\"authors\":\"Paloma T. Lima, Amir Nikabadi\",\"doi\":\"arxiv-2409.07366\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"A family $\\\\mathcal{F}$ of graphs is a \\\\textit{Gallai family} if for every\\nconnected graph $G\\\\in \\\\mathcal{F}$, all longest paths in $G$ have a common\\nvertex. While it is not known whether $P_5$-free graphs are a Gallai family,\\nLong Jr., Milans, and Munaro [The Electronic Journal of Combinatorics, 2023]\\nshowed that this is \\\\emph{not} the case for the class of claw-free graphs. We\\ngive a complete characterization of the graphs $H$ of size at most five for\\nwhich $(\\\\text{claw}, H)$-free graphs form a Gallai family. We also show that\\n$(P_5, H)$-free graphs form a Gallai family if $H$ is a triangle, a paw, or a\\ndiamond. Both of our results are constructive.\",\"PeriodicalId\":501407,\"journal\":{\"name\":\"arXiv - MATH - Combinatorics\",\"volume\":\"45 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-09-11\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"arXiv - MATH - Combinatorics\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/arxiv-2409.07366\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - MATH - Combinatorics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2409.07366","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Non-empty intersection of longest paths in $P_5$-free and claw-free graphs
A family $\mathcal{F}$ of graphs is a \textit{Gallai family} if for every
connected graph $G\in \mathcal{F}$, all longest paths in $G$ have a common
vertex. While it is not known whether $P_5$-free graphs are a Gallai family,
Long Jr., Milans, and Munaro [The Electronic Journal of Combinatorics, 2023]
showed that this is \emph{not} the case for the class of claw-free graphs. We
give a complete characterization of the graphs $H$ of size at most five for
which $(\text{claw}, H)$-free graphs form a Gallai family. We also show that
$(P_5, H)$-free graphs form a Gallai family if $H$ is a triangle, a paw, or a
diamond. Both of our results are constructive.