<p>A <i>k</i>-hypertournament <i>H</i> on <i>n</i> vertices is a pair (<i>V</i>(<i>H</i>),&#xa0;<i>A</i>(<i>H</i>)), where <i>V</i>(<i>H</i>) is a set of vertices and <i>A</i>(<i>H</i>) is a set of <i>k</i>-tuples of vertices, called arcs, such that for any <i>k</i>-subset <i>S</i> of <i>V</i>(<i>H</i>), <i>A</i>(<i>H</i>) contains exactly one of the <i>k</i>! <i>k</i>-tuples whose entries belong to <i>S</i>. Clearly, a 2-hypertournament is a tournament. An antidirected path in <i>H</i> is a sequence <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(x_1 a_1 x_2 a_2 x_3 \cdots x_{t-1} a_{t-1} x_t\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>x</mi> <mn>1</mn> </msub> <msub> <mi>a</mi> <mn>1</mn> </msub> <msub> <mi>x</mi> <mn>2</mn> </msub> <msub> <mi>a</mi> <mn>2</mn> </msub> <msub> <mi>x</mi> <mn>3</mn> </msub> <mo>⋯</mo> <msub> <mi>x</mi> <mrow> <mi>t</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <msub> <mi>a</mi> <mrow> <mi>t</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> <msub> <mi>x</mi> <mi>t</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> of distinct vertices <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(x_1, x_2, \ldots , x_t\)</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> <mo>…</mo> <mo>,</mo> <msub> <mi>x</mi> <mi>t</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> and distinct arcs <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(a_1, a_{2},\ldots , a_{t-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>a</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>a</mi> <mn>2</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>a</mi> <mrow> <mi>t</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> </mrow> </math></EquationSource> </InlineEquation> such that for any <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(i\in \{2,3,\ldots , t-1\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>i</mi> <mo>∈</mo> <mo stretchy="false">{</mo> <mn>2</mn> <mo>,</mo> <mn>3</mn> <mo>,</mo> <mo>…</mo> <mo>,</mo> <mi>t</mi> <mo>-</mo> <mn>1</mn> <mo stretchy="false">}</mo> </mrow> </math></EquationSource> </InlineEquation>, either <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(x_{i-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mrow> <mi>i</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> precedes <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(x_{i}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> in <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(a_{i-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>a</mi> <mrow> <mi>i</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(x_{i+1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mrow> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> precedes <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(x_{i}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> in <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(a_{i}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>a</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation>, or <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(x_{i}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> precedes <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(x_{i-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mrow> <mi>i</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> in <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(a_{i-1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>a</mi> <mrow> <mi>i</mi> <mo>-</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(x_{i}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> precedes <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(x_{i+1}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>x</mi> <mrow> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> </math></EquationSource> </InlineEquation> in <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(a_{i}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>a</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation>, but not both. An antidirected path that includes all vertices of a <i>k</i>-hypertournament <i>H</i> is known as an antidirected Hamilton path of <i>H</i>. In this paper, we prove that except for four <i>k</i>-hypertournaments, <InlineEquation ID="IEq17"> <EquationSource Format="TEX">\(T_3^{c}, T_5^{c}, T_7^{c}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>T</mi> <mn>3</mn> <mi>c</mi> </msubsup> <mo>,</mo> <msubsup> <mi>T</mi> <mn>5</mn> <mi>c</mi> </msubsup> <mo>,</mo> <msubsup> <mi>T</mi> <mn>7</mn> <mi>c</mi> </msubsup> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq18"> <EquationSource Format="TEX">\(H_{4}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>H</mi> <mn>4</mn> </msub> </math></EquationSource> </InlineEquation>, every <i>k</i>-hypertournament with <i>n</i> vertices, where <InlineEquation ID="IEq19"> <EquationSource Format="TEX">\(2\le k\le n-1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <mo>≤</mo> <mi>k</mi> <mo>≤</mo> <mi>n</mi> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, has an antidirected Hamilton path, which extends Grünbaum’s theorem on tournaments.</p>

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Antidirected Hamilton Paths in k-Hypertournaments

  • Hong Yang,
  • Changchang Dong,
  • Jixiang Meng,
  • Juan Liu

摘要

A k-hypertournament H on n vertices is a pair (V(H), A(H)), where V(H) is a set of vertices and A(H) is a set of k-tuples of vertices, called arcs, such that for any k-subset S of V(H), A(H) contains exactly one of the k! k-tuples whose entries belong to S. Clearly, a 2-hypertournament is a tournament. An antidirected path in H is a sequence \(x_1 a_1 x_2 a_2 x_3 \cdots x_{t-1} a_{t-1} x_t\) x 1 a 1 x 2 a 2 x 3 x t - 1 a t - 1 x t of distinct vertices \(x_1, x_2, \ldots , x_t\) x 1 , x 2 , , x t and distinct arcs \(a_1, a_{2},\ldots , a_{t-1}\) a 1 , a 2 , , a t - 1 such that for any \(i\in \{2,3,\ldots , t-1\}\) i { 2 , 3 , , t - 1 } , either \(x_{i-1}\) x i - 1 precedes \(x_{i}\) x i in \(a_{i-1}\) a i - 1 and \(x_{i+1}\) x i + 1 precedes \(x_{i}\) x i in \(a_{i}\) a i , or \(x_{i}\) x i precedes \(x_{i-1}\) x i - 1 in \(a_{i-1}\) a i - 1 and \(x_{i}\) x i precedes \(x_{i+1}\) x i + 1 in \(a_{i}\) a i , but not both. An antidirected path that includes all vertices of a k-hypertournament H is known as an antidirected Hamilton path of H. In this paper, we prove that except for four k-hypertournaments, \(T_3^{c}, T_5^{c}, T_7^{c}\) T 3 c , T 5 c , T 7 c and \(H_{4}\) H 4 , every k-hypertournament with n vertices, where \(2\le k\le n-1\) 2 k n - 1 , has an antidirected Hamilton path, which extends Grünbaum’s theorem on tournaments.