• Title/Summary/Keyword: semicomplete digraph

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LOCALLY SEMICOMPLETE DIGRAPHS WITH A FACTOR COMPOSED OF k CYCLES

  • Gould, Ronald J.;Guo, Yubao
    • Journal of the Korean Mathematical Society
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    • v.41 no.5
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    • pp.895-912
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    • 2004
  • A digraph is locally semicomplete if for every vertex $\chi$, the set of in-neighbors as well as the set of out-neighbors of $\chi$ induce semicomplete digraphs. Let D be a k-connected locally semicomplete digraph with k $\geq$ 3 and g denote the length of a longest induced cycle of D. It is shown that if D has at least 7(k-1)g vertices, then D has a factor composed of k cycles; furthermore, if D is semicomplete and with at least 5k + 1 vertices, then D has a factor composed of k cycles and one of the cycles is of length at most 5. Our results generalize those of [3] for tournaments to locally semicomplete digraphs.

PANCYCLIC ARCS IN HAMILTONIAN CYCLES OF HYPERTOURNAMENTS

  • Guo, Yubao;Surmacs, Michel
    • Journal of the Korean Mathematical Society
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    • v.51 no.6
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    • pp.1141-1154
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    • 2014
  • A k-hypertournament H on n vertices, where $2{\leq}k{\leq}n$, is a pair H = (V,A), where V is the vertex set of H and A is a set of k-tuples of vertices, called arcs, such that for all subsets $S{\subseteq}V$ with |S| = k, A contains exactly one permutation of S as an arc. Recently, Li et al. showed that any strong k-hypertournament H on n vertices, where $3{\leq}k{\leq}n-2$, is vertex-pancyclic, an extension of Moon's theorem for tournaments. In this paper, we prove the following generalization of another of Moon's theorems: If H is a strong k-hypertournament on n vertices, where $3{\leq}k{\leq}n-2$, and C is a Hamiltonian cycle in H, then C contains at least three pancyclic arcs.