Compression and Erdös-Ko-Rado graphs

نویسندگان

  • Fred C. Holroyd
  • Claire Spencer
  • John M. Talbot
چکیده

For a graph G and integer r ≥ 1 we denote the collection of independent r-sets of G by I (r)(G). If v ∈ V (G) then I (r) v (G) is the collection of all independent r-sets containing v. A graph G, is said to be r-EKR, for r ≥ 1, iff no intersecting family A ⊆ I (r)(G) is larger than maxv∈V (G) |I v (G)|. There are various graphs which are known to have his property: the empty graph of order n ≥ 2r (this is the celebrated Erdős-Ko-Rado theorem), any disjoint union of at least r copies of Kt for t ≥ 2, and any cycle. In this paper we show how these results can be extended to other classes of graphs via a compression proof technique. In particular we extend a theorem of Berge [2], showing that any disjoint union of at least r complete graphs, each of order at least two, is r-EKR. We also show that paths are r-EKR for all r ≥ 1.

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عنوان ژورنال:
  • Discrete Mathematics

دوره 293  شماره 

صفحات  -

تاریخ انتشار 2005