Four-cycles in graphs without a given even cycle

  • Authors:
  • Daniela Kühn;Deryk Osthus

  • Affiliations:
  • Freie Universität Berlin, Institut für Mathematik, Arnimallee 2–6, D-14195 Berlin, Germany;Institut für Informatik, Humboldt-Universität zu Berlin, Unter den Linden 6, D-10099 Berlin, Germany

  • Venue:
  • Journal of Graph Theory
  • Year:
  • 2005

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Abstract

We prove that every bipartite C2l-freegraph G contains a C4-free subgraphH with e(H) ≥ e(G)-(l1). The factor 1-(l 1) is best possible. This implies thatex(n, C2l) ≤ 2(l1)ex(n, {C4,C2l}), which settles a special case of aconjecture of Erdõs and Simonovits. © 2004 WileyPeriodicals, Inc. J Graph Theory 48: 147156, 2005