Linkedness and ordered cycles in digraphs

  • Authors:
  • Daniela KÜhn;Deryk Osthus

  • Affiliations:
  • School of mathematics, university of birmingham, edgbaston, birmingham, b15 2tt, uk (e-mail: kuehn@maths.bham.ac.uk, osthus@maths.bham.ac.uk);School of mathematics, university of birmingham, edgbaston, birmingham, b15 2tt, uk (e-mail: kuehn@maths.bham.ac.uk, osthus@maths.bham.ac.uk)

  • Venue:
  • Combinatorics, Probability and Computing
  • Year:
  • 2008

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Abstract

Given a digraph D, let δ0(D) := min{δ+(D), δ−(D)} be the minimum semi-degree of D. We show that every sufficiently large digraph D with δ0(D)≥n/2 + l −1 is l-linked. The bound on the minimum semi-degree is best possible and confirms a conjecture of Manoussakis [17]. We also determine the smallest minimum semi-degree which ensures that a sufficiently large digraph D is k-ordered, i.e., that for every sequence s1,. . ., sk of distinct vertices of D there is a directed cycle which encounters s1,. . ., sk in this order. This result will be used in [16].