139 research outputs found

    A note on tilted Sperner families with patterns

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    Let pp and qq be two nonnegative integers with p+q>0p+q>0 and n>0n>0. We call FP([n])\mathcal{F} \subset \mathcal{P}([n]) a \textit{(p,q)-tilted Sperner family with patterns on [n]} if there are no distinct F,GFF,G \in \mathcal{F} with: (i)  pFG=qGF, and(i) \ \ p|F \setminus G|=q|G \setminus F|, \ \textrm{and} (ii) f>g for all fFG and gGF.(ii) \ f > g \ \textrm{for all} \ f \in F \setminus G \ \textrm{and} \ g \in G \setminus F. Long (\cite{L}) proved that the cardinality of a (1,2)-tilted Sperner family with patterns on [n][n] is O(e120logn 2nn).O(e^{120\sqrt{\log n}}\ \frac{2^n}{\sqrt{n}}). We improve and generalize this result, and prove that the cardinality of every (p,qp,q)-tilted Sperner family with patterns on [nn] is O(logn 2nn).O(\sqrt{\log n} \ \frac{2^n}{\sqrt{n}}).Comment: 8 page

    On Tur\'an problems with bounded matching number

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    Very recently, Alon and Frankl initiated the study of the maximum number of edges in nn-vertex FF-free graphs with matching number at most ss. For fixed FF and ss, we determine this number apart from a constant additive term. We also obtain several exact results

    Rainbow copies of FF in families of HH

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    We study the following problem. How many distinct copies of HH can an nn-vertex graph GG have, if GG does not contain a rainbow FF, that is, a copy of FF where each edge is contained in a different copy of HH? The case H=KrH=K_r is equivalent to the Tur\'an problem for Berge hypergraphs, which has attracted several researchers recently. We also explore the connection of our problem to the so-called generalized Tur\'an problems. We obtain several exact results. In the particularly interesting symmetric case where H=FH=F, we completely solve the case FF is the 3-edge path, and asymptitically solve the case FF is a book graph
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