{"title":"Planar Graphs without Cycles of Length 3, 4, and 6 are (3, 3)-Colorable","authors":"Pongpat Sittitrai, W. Pimpasalee","doi":"10.1155/2024/7884281","DOIUrl":null,"url":null,"abstract":"<jats:p>For non-negative integers <jats:inline-formula><a:math xmlns:a=\"http://www.w3.org/1998/Math/MathML\" id=\"M1\"><a:msub><a:mrow><a:mi>d</a:mi></a:mrow><a:mrow><a:mn>1</a:mn></a:mrow></a:msub></a:math></jats:inline-formula> and <jats:inline-formula><c:math xmlns:c=\"http://www.w3.org/1998/Math/MathML\" id=\"M2\"><c:msub><c:mrow><c:mi>d</c:mi></c:mrow><c:mrow><c:mn>2</c:mn></c:mrow></c:msub></c:math></jats:inline-formula>, if <jats:inline-formula><e:math xmlns:e=\"http://www.w3.org/1998/Math/MathML\" id=\"M3\"><e:msub><e:mrow><e:mi>V</e:mi></e:mrow><e:mrow><e:mn>1</e:mn></e:mrow></e:msub></e:math></jats:inline-formula> and <jats:inline-formula><g:math xmlns:g=\"http://www.w3.org/1998/Math/MathML\" id=\"M4\"><g:msub><g:mrow><g:mi>V</g:mi></g:mrow><g:mrow><g:mn>2</g:mn></g:mrow></g:msub></g:math></jats:inline-formula> are two partitions of a graph <jats:inline-formula><i:math xmlns:i=\"http://www.w3.org/1998/Math/MathML\" id=\"M5\"><i:mi>G</i:mi></i:math></jats:inline-formula>’s vertex set <jats:inline-formula><k:math xmlns:k=\"http://www.w3.org/1998/Math/MathML\" id=\"M6\"><k:mi>V</k:mi><k:mfenced open=\"(\" close=\")\" separators=\"|\"><k:mrow><k:mi>G</k:mi></k:mrow></k:mfenced></k:math></jats:inline-formula>, such that <jats:inline-formula><p:math xmlns:p=\"http://www.w3.org/1998/Math/MathML\" id=\"M7\"><p:msub><p:mrow><p:mi>V</p:mi></p:mrow><p:mrow><p:mn>1</p:mn></p:mrow></p:msub></p:math></jats:inline-formula> and <jats:inline-formula><r:math xmlns:r=\"http://www.w3.org/1998/Math/MathML\" id=\"M8\"><r:msub><r:mrow><r:mi>V</r:mi></r:mrow><r:mrow><r:mn>2</r:mn></r:mrow></r:msub></r:math></jats:inline-formula> induce two subgraphs of <jats:inline-formula><t:math xmlns:t=\"http://www.w3.org/1998/Math/MathML\" id=\"M9\"><t:mi>G</t:mi></t:math></jats:inline-formula>, called <jats:inline-formula><v:math xmlns:v=\"http://www.w3.org/1998/Math/MathML\" id=\"M10\"><v:mi>G</v:mi><v:mfenced open=\"[\" close=\"]\" separators=\"|\"><v:mrow><v:msub><v:mrow><v:mi>V</v:mi></v:mrow><v:mrow><v:mn>1</v:mn></v:mrow></v:msub></v:mrow></v:mfenced></v:math></jats:inline-formula> with maximum degree at most <jats:inline-formula><ab:math xmlns:ab=\"http://www.w3.org/1998/Math/MathML\" id=\"M11\"><ab:msub><ab:mrow><ab:mi>d</ab:mi></ab:mrow><ab:mrow><ab:mn>1</ab:mn></ab:mrow></ab:msub></ab:math></jats:inline-formula> and <jats:inline-formula><cb:math xmlns:cb=\"http://www.w3.org/1998/Math/MathML\" id=\"M12\"><cb:mi>G</cb:mi><cb:mfenced open=\"[\" close=\"]\" separators=\"|\"><cb:mrow><cb:msub><cb:mrow><cb:mi>V</cb:mi></cb:mrow><cb:mrow><cb:mn>2</cb:mn></cb:mrow></cb:msub></cb:mrow></cb:mfenced></cb:math></jats:inline-formula> with maximum degree at most <jats:inline-formula><hb:math xmlns:hb=\"http://www.w3.org/1998/Math/MathML\" id=\"M13\"><hb:msub><hb:mrow><hb:mi>d</hb:mi></hb:mrow><hb:mrow><hb:mn>2</hb:mn></hb:mrow></hb:msub></hb:math></jats:inline-formula>, respectively, then the graph <jats:inline-formula><jb:math xmlns:jb=\"http://www.w3.org/1998/Math/MathML\" id=\"M14\"><jb:mi>G</jb:mi></jb:math></jats:inline-formula> is said to be improper <jats:inline-formula><lb:math xmlns:lb=\"http://www.w3.org/1998/Math/MathML\" id=\"M15\"><lb:mfenced open=\"(\" close=\")\" separators=\"|\"><lb:mrow><lb:msub><lb:mrow><lb:mi>d</lb:mi></lb:mrow><lb:mrow><lb:mn>1</lb:mn></lb:mrow></lb:msub><lb:mo>,</lb:mo><lb:msub><lb:mrow><lb:mi>d</lb:mi></lb:mrow><lb:mrow><lb:mn>2</lb:mn></lb:mrow></lb:msub></lb:mrow></lb:mfenced></lb:math></jats:inline-formula>-colorable, as well as <jats:inline-formula><qb:math xmlns:qb=\"http://www.w3.org/1998/Math/MathML\" id=\"M16\"><qb:mfenced open=\"(\" close=\")\" separators=\"|\"><qb:mrow><qb:msub><qb:mrow><qb:mi>d</qb:mi></qb:mrow><qb:mrow><qb:mn>1</qb:mn></qb:mrow></qb:msub><qb:mo>,</qb:mo><qb:msub><qb:mrow><qb:mi>d</qb:mi></qb:mrow><qb:mrow><qb:mn>2</qb:mn></qb:mrow></qb:msub></qb:mrow></qb:mfenced></qb:math></jats:inline-formula>-colorable. A class of planar graphs without <jats:inline-formula><vb:math xmlns:vb=\"http://www.w3.org/1998/Math/MathML\" id=\"M17\"><vb:msub><vb:mrow><vb:mi>C</vb:mi></vb:mrow><vb:mrow><vb:mn>3</vb:mn></vb:mrow></vb:msub><vb:mo>,</vb:mo><vb:msub><vb:mrow><vb:mi>C</vb:mi></vb:mrow><vb:mrow><vb:mn>4</vb:mn></vb:mrow></vb:msub></vb:math></jats:inline-formula>, and <jats:inline-formula><xb:math xmlns:xb=\"http://www.w3.org/1998/Math/MathML\" id=\"M18\"><xb:msub><xb:mrow><xb:mi>C</xb:mi></xb:mrow><xb:mrow><xb:mn>6</xb:mn></xb:mrow></xb:msub></xb:math></jats:inline-formula> is denoted by <jats:inline-formula><zb:math xmlns:zb=\"http://www.w3.org/1998/Math/MathML\" id=\"M19\"><zb:mi mathvariant=\"script\">C</zb:mi></zb:math></jats:inline-formula>. In 2019, Dross and Ochem proved that <jats:inline-formula><cc:math xmlns:cc=\"http://www.w3.org/1998/Math/MathML\" id=\"M20\"><cc:mi>G</cc:mi></cc:math></jats:inline-formula> is <jats:inline-formula><ec:math xmlns:ec=\"http://www.w3.org/1998/Math/MathML\" id=\"M21\"><ec:mfenced open=\"(\" close=\")\" separators=\"|\"><ec:mrow><ec:mn>0</ec:mn><ec:mo>,</ec:mo><ec:mn>6</ec:mn></ec:mrow></ec:mfenced></ec:math></jats:inline-formula>-colorable, for each graph <jats:inline-formula><jc:math xmlns:jc=\"http://www.w3.org/1998/Math/MathML\" id=\"M22\"><jc:mi>G</jc:mi></jc:math></jats:inline-formula> in <jats:inline-formula><lc:math xmlns:lc=\"http://www.w3.org/1998/Math/MathML\" id=\"M23\"><lc:mi mathvariant=\"script\">C</lc:mi></lc:math></jats:inline-formula>. Given that <jats:inline-formula><oc:math xmlns:oc=\"http://www.w3.org/1998/Math/MathML\" id=\"M24\"><oc:msub><oc:mrow><oc:mi>d</oc:mi></oc:mrow><oc:mrow><oc:mn>1</oc:mn></oc:mrow></oc:msub><oc:mo>+</oc:mo><oc:msub><oc:mrow><oc:mi>d</oc:mi></oc:mrow><oc:mrow><oc:mn>2</oc:mn></oc:mrow></oc:msub><oc:mo>≥</oc:mo><oc:mn>6</oc:mn></oc:math></jats:inline-formula>, this inspires us to investigate whether <jats:inline-formula><qc:math xmlns:qc=\"http://www.w3.org/1998/Math/MathML\" id=\"M25\"><qc:mi>G</qc:mi></qc:math></jats:inline-formula> is <jats:inline-formula><sc:math xmlns:sc=\"http://www.w3.org/1998/Math/MathML\" id=\"M26\"><sc:mfenced open=\"(\" close=\")\" separators=\"|\"><sc:mrow><sc:msub><sc:mrow><sc:mi>d</sc:mi></sc:mrow><sc:mrow><sc:mn>1</sc:mn></sc:mrow></sc:msub><sc:mo>,</sc:mo><sc:msub><sc:mrow><sc:mi>d</sc:mi></sc:mrow><sc:mrow><sc:mn>2</sc:mn></sc:mrow></sc:msub></sc:mrow></sc:mfenced></sc:math></jats:inline-formula>-colorable, for each graph <jats:inline-formula><xc:math xmlns:xc=\"http://www.w3.org/1998/Math/MathML\" id=\"M27\"><xc:mi>G</xc:mi></xc:math></jats:inline-formula> in <jats:inline-formula><zc:math xmlns:zc=\"http://www.w3.org/1998/Math/MathML\" id=\"M28\"><zc:mi mathvariant=\"script\">C</zc:mi></zc:math></jats:inline-formula>. In this paper, we provide a partial solution by showing that <jats:inline-formula><cd:math xmlns:cd=\"http://www.w3.org/1998/Math/MathML\" id=\"M29\"><cd:mi>G</cd:mi></cd:math></jats:inline-formula> is (3, 3)-colorable, for each graph <jats:inline-formula><ed:math xmlns:ed=\"http://www.w3.org/1998/Math/MathML\" id=\"M30\"><ed:mi>G</ed:mi></ed:math></jats:inline-formula> in <jats:inline-formula><gd:math xmlns:gd=\"http://www.w3.org/1998/Math/MathML\" id=\"M31\"><gd:mi mathvariant=\"script\">C</gd:mi></gd:math></jats:inline-formula>.</jats:p>","PeriodicalId":509297,"journal":{"name":"International Journal of Mathematics and Mathematical Sciences","volume":" 21","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"International Journal of Mathematics and Mathematical Sciences","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1155/2024/7884281","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
For non-negative integers d1 and d2, if V1 and V2 are two partitions of a graph G’s vertex set VG, such that V1 and V2 induce two subgraphs of G, called GV1 with maximum degree at most d1 and GV2 with maximum degree at most d2, respectively, then the graph G is said to be improper d1,d2-colorable, as well as d1,d2-colorable. A class of planar graphs without C3,C4, and C6 is denoted by C. In 2019, Dross and Ochem proved that G is 0,6-colorable, for each graph G in C. Given that d1+d2≥6, this inspires us to investigate whether G is d1,d2-colorable, for each graph G in C. In this paper, we provide a partial solution by showing that G is (3, 3)-colorable, for each graph G in C.