Three supplements to Reid's theorem in multipartite tournaments

  • Authors:
  • Shengjia Li;Wei Meng;Yubao Guo

  • Affiliations:
  • School of Mathematical Sciences, Shanxi University, 030006 Taiyuan, PR China;School of Mathematical Sciences, Shanxi University, 030006 Taiyuan, PR China;Lehrstuhl C für Mathematik, RWTH Aachen University, 52056 Aachen, Germany

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2010

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Abstract

An n-partite tournament is an orientation of a complete n-partite graph. In this paper, we give three supplements to Reid's theorem [K.B. Reid, Two complementary circuits in two-connected tournaments, Ann. Discrete Math. 27 (1985) 321-334] in multipartite tournaments. The first one is concerned with the lengths of cycles and states as follows: let D be an (@a(D)+1)-strong n-partite tournament with n=6, where @a(D) is the independence number of D, then D contains two disjoint cycles of lengths 3 and n-3, respectively, unless D is isomorphic to the 7-tournament containing no transitive 4-subtournament (denoted by T"7^1). The second one is obtained by considering the number of partite sets that cycles pass through: every (@a(D)+1)-strong n-partite tournament D with n=6 contains two disjoint cycles which contain vertices from exactly 3 and n-3 partite sets, respectively, unless it is isomorphic to T"7^1. The last one is about two disjoint cycles passing through all partite sets.