The maximum size of intersecting and union families of sets
نویسندگان
چکیده
We consider the maximal size of families of k-element subsets of an n element set [n] = {1, 2, . . . , n} that satisfy the properties that every r subsets of the family have non-empty intersection, and no ` subsets contain [n] in their union. We show that for large enough n, the largest such family is the trivial one of all ( n−2 k−1 ) subsets that contain a given element and do not contain another given element. Moreover we show that unless such a family is such that all subsets contain a given element, or all subsets miss a given element, then it has size at most .9 ( n−2 k−1 ) . We also obtain versions of these statements for weighted non-uniform families.
منابع مشابه
Almost Intersecting Families of Sets
Let us write DF (G) = {F ∈ F : F ∩ G = ∅} for a set G and a family F . Then a family F of sets is said to be (≤ l)-almost intersecting (l-almost intersecting) if for any F ∈ F we have |DF (F )| ≤ l (|DF (F )| = l). In this paper we investigate the problem of finding the maximum size of an (≤ l)almost intersecting (l-almost intersecting) family F . AMS Subject Classification: 05D05
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ورودعنوان ژورنال:
- Eur. J. Comb.
دوره 33 شماره
صفحات -
تاریخ انتشار 2012