<p>Let <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq3.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(k \ge 5\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>≥</mo> <mn>5</mn> </mrow> </math></EquationSource> </InlineEquation> be an odd integer and <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq4.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="135" /> </InlineMediaObject> <EquationSource Format="TEX">\(G=(V(G),E(G))\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>G</mi> <mo>=</mo> <mo stretchy="false">(</mo> <mi>V</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> <mo>,</mo> <mi>E</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> be a <i>k</i>-edge-connected graph. For <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq5.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="79" /> </InlineMediaObject> <EquationSource Format="TEX">\(X\subseteq V(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>X</mi> <mo>⊆</mo> <mi>V</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, <i>e</i>(<i>X</i>) denotes the number of edges between <i>X</i> and <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq6.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="79" /> </InlineMediaObject> <EquationSource Format="TEX">\(V(G)-X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>V</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> <mo>-</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation>. We here prove that if <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq7.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="154" /> </InlineMediaObject> <EquationSource Format="TEX">\(\{s_i,t_i\}\subseteq X_i\subseteq V(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">{</mo> <msub> <mi>s</mi> <mi>i</mi> </msub> <mo>,</mo> <msub> <mi>t</mi> <mi>i</mi> </msub> <mo stretchy="false">}</mo> </mrow> <mo>⊆</mo> <msub> <mi>X</mi> <mi>i</mi> </msub> <mo>⊆</mo> <mi>V</mi> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq8.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(f_1\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>f</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation> is an edge between <InlineEquation ID="IEq9"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq9.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(s_1\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>s</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq10"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq10.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(s_2\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>s</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq11"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq11.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(f_2\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>f</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation> is an edge between <InlineEquation ID="IEq12"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq12.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(t_1\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>t</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq13"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq13.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(t_2\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>t</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq14"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq14.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="109" /> </InlineMediaObject> <EquationSource Format="TEX">\(e(X_i)\le 2k-3\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>e</mi> <mo stretchy="false">(</mo> <msub> <mi>X</mi> <mi>i</mi> </msub> <mo stretchy="false">)</mo> <mo>≤</mo> <mn>2</mn> <mi>k</mi> <mo>-</mo> <mn>3</mn> </mrow> </math></EquationSource> </InlineEquation>&#xa0; <InlineEquation ID="IEq15"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq15.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="65" /> </InlineMediaObject> <EquationSource Format="TEX">\((i=1,2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq16"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq16.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="95" /> </InlineMediaObject> <EquationSource Format="TEX">\(X_1\cap X_2=\emptyset\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>X</mi> <mn>1</mn> </msub> <mo>∩</mo> <msub> <mi>X</mi> <mn>2</mn> </msub> <mo>=</mo> <mi mathvariant="normal">∅</mi> </mrow> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq17"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq17.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="96" /> </InlineMediaObject> <EquationSource Format="TEX">\(e(Y)\ge k+2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>e</mi> <mo stretchy="false">(</mo> <mi>Y</mi> <mo stretchy="false">)</mo> <mo>≥</mo> <mi>k</mi> <mo>+</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation> for each <InlineEquation ID="IEq18"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq18.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="77" /> </InlineMediaObject> <EquationSource Format="TEX">\(Y\subseteq V(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>Y</mi> <mo>⊆</mo> <mi>V</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> with <InlineEquation ID="IEq19"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq19.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="204" /> </InlineMediaObject> <EquationSource Format="TEX">\(Y\cap \{s_1,t_1,s_2,t_2\}=\{s_1,t_2\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>Y</mi> <mo>∩</mo> <mrow> <mo stretchy="false">{</mo> <msub> <mi>s</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>t</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>s</mi> <mn>2</mn> </msub> <mo>,</mo> <msub> <mi>t</mi> <mn>2</mn> </msub> <mo stretchy="false">}</mo> </mrow> <mo>=</mo> <mrow> <mo stretchy="false">{</mo> <msub> <mi>s</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>t</mi> <mn>2</mn> </msub> <mo stretchy="false">}</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, then there exist paths <InlineEquation ID="IEq20"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq20.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(P_1\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>P</mi> <mn>1</mn> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq21"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq21.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(P_2\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>P</mi> <mn>2</mn> </msub> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq22"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq22.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="19" /> </InlineMediaObject> <EquationSource Format="TEX">\(P_i\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>P</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> joins <InlineEquation ID="IEq23"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq23.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="16" /> </InlineMediaObject> <EquationSource Format="TEX">\(s_i\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>s</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq24"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq24.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="14" /> </InlineMediaObject> <EquationSource Format="TEX">\(t_i\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>t</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation>, <InlineEquation ID="IEq25"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq25.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="86" /> </InlineMediaObject> <EquationSource Format="TEX">\(V(P_i)\subseteq X_i\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>V</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>P</mi> <mi>i</mi> </msub> <mo stretchy="false">)</mo> </mrow> <mo>⊆</mo> <msub> <mi>X</mi> <mi>i</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>&#xa0; (<InlineEquation ID="IEq26"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq26.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="53" /> </InlineMediaObject> <EquationSource Format="TEX">\(i=1,2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>) and <InlineEquation ID="IEq27"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq27.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="190" /> </InlineMediaObject> <EquationSource Format="TEX">\(G-\{f_1,f_2\}-E(P_1\cup P_2)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>G</mi> <mo>-</mo> <mrow> <mo stretchy="false">{</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo stretchy="false">}</mo> </mrow> <mo>-</mo> <mi>E</mi> <mrow> <mo stretchy="false">(</mo> <msub> <mi>P</mi> <mn>1</mn> </msub> <mo>∪</mo> <msub> <mi>P</mi> <mn>2</mn> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> is (<InlineEquation ID="IEq28"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="373_2024_2873_Article_IEq28.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="40" /> </InlineMediaObject> <EquationSource Format="TEX">\(k-2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>-</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>)-edge-connected, and in fact we give a generalization of this result.</p>

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2-Reducible Two Paths and Two Edges Constructing a Cycle in \((2k+1)\)-Edge-Connected Graphs

  • Haruko Okamura

摘要

Let \(k \ge 5\) k 5 be an odd integer and \(G=(V(G),E(G))\) G = ( V ( G ) , E ( G ) ) be a k-edge-connected graph. For \(X\subseteq V(G)\) X V ( G ) , e(X) denotes the number of edges between X and \(V(G)-X\) V ( G ) - X . We here prove that if \(\{s_i,t_i\}\subseteq X_i\subseteq V(G)\) { s i , t i } X i V ( G ) , \(f_1\) f 1 is an edge between \(s_1\) s 1 and \(s_2\) s 2 , \(f_2\) f 2 is an edge between \(t_1\) t 1 and \(t_2\) t 2 , \(e(X_i)\le 2k-3\) e ( X i ) 2 k - 3   \((i=1,2)\) ( i = 1 , 2 ) , \(X_1\cap X_2=\emptyset\) X 1 X 2 = , and \(e(Y)\ge k+2\) e ( Y ) k + 2 for each \(Y\subseteq V(G)\) Y V ( G ) with \(Y\cap \{s_1,t_1,s_2,t_2\}=\{s_1,t_2\}\) Y { s 1 , t 1 , s 2 , t 2 } = { s 1 , t 2 } , then there exist paths \(P_1\) P 1 and \(P_2\) P 2 such that \(P_i\) P i joins \(s_i\) s i and \(t_i\) t i , \(V(P_i)\subseteq X_i\) V ( P i ) X i   ( \(i=1,2\) i = 1 , 2 ) and \(G-\{f_1,f_2\}-E(P_1\cup P_2)\) G - { f 1 , f 2 } - E ( P 1 P 2 ) is ( \(k-2\) k - 2 )-edge-connected, and in fact we give a generalization of this result.