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A Ramsey-Sperner theorem
Authors:Z Füredi
Institution:(1) Mathematical Institute of the Hungarian Academy of Science, P.O.B. 127, H-1364 Budapest, Hungary
Abstract:Letnk≥1 be integers and letf(n, k) be the smallest integer for which the following holds: If ℱ is a family of subsets of ann-setX with |ℱ|<f(n,k) then for everyk-coloring ofX there existA B ∈ ℱ,A∈B, A⊂B such thatB-A is monochromatic. Here it is proven that for a fixedk there exist constantsc k andd k such that 
$$c_k (1 + o(1))< f(n,k)\sqrt {{n \mathord{\left/ {\vphantom {n {2^a }}} \right. \kern-\nulldelimiterspace} {2^a }}}< d_k (1 + o(1))$$
and 
$$c_k  = \sqrt {{k \mathord{\left/ {\vphantom {k {2\log k}}} \right. \kern-\nulldelimiterspace} {2\log k}}} (1 + o(1)) = d_k $$
ask→∞. The proofs of both the lower and the upper bounds use probabilistic methods.
Keywords:
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