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{"title":"Highly connected triples and Mader's conjecture","authors":"Qinghai Liu, Kai Ying, Yanmei Hong","doi":"10.1002/jgt.23144","DOIUrl":null,"url":null,"abstract":"<p>Mader proved that, for any tree <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>T</mi>\n </mrow>\n </mrow>\n <annotation> $T$</annotation>\n </semantics></math> of order <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>m</mi>\n </mrow>\n </mrow>\n <annotation> $m$</annotation>\n </semantics></math>, every <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>k</mi>\n </mrow>\n </mrow>\n <annotation> $k$</annotation>\n </semantics></math>-connected graph <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n </mrow>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> with <span></span><math>\n <semantics>\n <mrow>\n \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 <mn>2</mn>\n \n <msup>\n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>k</mi>\n \n <mo>+</mo>\n \n <mi>m</mi>\n \n <mo>−</mo>\n \n <mn>1</mn>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n \n <mn>2</mn>\n </msup>\n \n <mo>+</mo>\n \n <mi>m</mi>\n \n <mo>−</mo>\n \n <mn>1</mn>\n </mrow>\n </mrow>\n <annotation> $\\delta (G)\\ge 2{(k+m-1)}^{2}+m-1$</annotation>\n </semantics></math> contains a subtree <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <msup>\n <mi>T</mi>\n \n <mo>′</mo>\n </msup>\n \n <mo>≅</mo>\n \n <mi>T</mi>\n </mrow>\n </mrow>\n <annotation> ${T}^{^{\\prime} }\\cong T$</annotation>\n </semantics></math> such that <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n \n <mo>−</mo>\n \n <mi>V</mi>\n \n <mrow>\n <mo>(</mo>\n \n <msup>\n <mi>T</mi>\n \n <mo>′</mo>\n </msup>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n </mrow>\n <annotation> $G-V({T}^{^{\\prime} })$</annotation>\n </semantics></math> is <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>k</mi>\n </mrow>\n </mrow>\n <annotation> $k$</annotation>\n </semantics></math>-connected. We proved that any graph <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n </mrow>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> with minimum degree <span></span><math>\n <semantics>\n <mrow>\n \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 <mn>2</mn>\n \n <mi>k</mi>\n </mrow>\n </mrow>\n <annotation> $\\delta (G)\\ge 2k$</annotation>\n </semantics></math> contains <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>k</mi>\n </mrow>\n </mrow>\n <annotation> $k$</annotation>\n </semantics></math>-connected triples. As a corollary, we prove that, for any tree <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>T</mi>\n </mrow>\n </mrow>\n <annotation> $T$</annotation>\n </semantics></math> of order <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>m</mi>\n </mrow>\n </mrow>\n <annotation> $m$</annotation>\n </semantics></math>, every <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>k</mi>\n </mrow>\n </mrow>\n <annotation> $k$</annotation>\n </semantics></math>-connected graph <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n </mrow>\n </mrow>\n <annotation> $G$</annotation>\n </semantics></math> with <span></span><math>\n <semantics>\n <mrow>\n \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 <mn>3</mn>\n \n <mi>k</mi>\n \n <mo>+</mo>\n \n <mn>4</mn>\n \n <mi>m</mi>\n \n <mo>−</mo>\n \n <mn>6</mn>\n </mrow>\n </mrow>\n <annotation> $\\delta (G)\\ge 3k+4m-6$</annotation>\n </semantics></math> contains a subtree <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <msup>\n <mi>T</mi>\n \n <mo>′</mo>\n </msup>\n \n <mo>≅</mo>\n \n <mi>T</mi>\n </mrow>\n </mrow>\n <annotation> ${T}^{^{\\prime} }\\cong T$</annotation>\n </semantics></math> such that <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>G</mi>\n \n <mo>−</mo>\n \n <mi>V</mi>\n \n <mrow>\n <mo>(</mo>\n \n <msup>\n <mi>T</mi>\n \n <mo>′</mo>\n </msup>\n \n <mo>)</mo>\n </mrow>\n </mrow>\n </mrow>\n <annotation> $G-V({T}^{^{\\prime} })$</annotation>\n </semantics></math> is still <span></span><math>\n <semantics>\n <mrow>\n \n <mrow>\n <mi>k</mi>\n </mrow>\n </mrow>\n <annotation> $k$</annotation>\n </semantics></math>-connected, improving Mader's condition to a linear bound.</p>","PeriodicalId":0,"journal":{"name":"","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"","FirstCategoryId":"100","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23144","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
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Abstract
Mader proved that, for any tree
T
$T$
of order
m
$m$
, every
k
$k$
-connected graph
G
$G$
with
δ
(
G
)
≥
2
(
k
+
m
−
1
)
2
+
m
−
1
$\delta (G)\ge 2{(k+m-1)}^{2}+m-1$
contains a subtree
T
′
≅
T
${T}^{^{\prime} }\cong T$
such that
G
−
V
(
T
′
)
$G-V({T}^{^{\prime} })$
is
k
$k$
-connected. We proved that any graph
G
$G$
with minimum degree
δ
(
G
)
≥
2
k
$\delta (G)\ge 2k$
contains
k
$k$
-connected triples. As a corollary, we prove that, for any tree
T
$T$
of order
m
$m$
, every
k
$k$
-connected graph
G
$G$
with
δ
(
G
)
≥
3
k
+
4
m
−
6
$\delta (G)\ge 3k+4m-6$
contains a subtree
T
′
≅
T
${T}^{^{\prime} }\cong T$
such that
G
−
V
(
T
′
)
$G-V({T}^{^{\prime} })$
is still
k
$k$
-connected, improving Mader's condition to a linear bound.
高连接三元组和马德猜想
作为推论,我们证明对于任何阶数为 m $m$ 的树 T $T$ ,每一个 k $k$ -connected graph G $G$ δ ( G ) ≥ 3 k + 4 m - 6 $\delta (G)\ge 3k+4m-6$ 都包含一个子树 T ′ ≅ T ${T}^{^{\prime} }\cong T$,使得 G - V ( T ′ ) $G-V({T}^{^{\prime} })$ 仍然是 k $k$ -connected 的,从而将马德的条件改进为线性约束。
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