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تسجيل مستخدم جديدA note on hypergraphs without non-trivial intersecting subgraphs
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تأليف
Xizhi Liu
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A hypergraph $mathcal{F}$ is non-trivial intersecting if every two edges in it have a nonempty intersection but no vertex is contained in all edges of $mathcal{F}$. Mubayi and Verstra{e}te showed that for every $k ge d+1 ge 3$ and $n ge (d+1)n/d$ every $k$-graph $mathcal{H}$ on $n$ vertices without a non-trivial intersecting subgraph of size $d+1$ contains at most $binom{n-1}{k-1}$ edges. They conjectured that the same conclusion holds for all $d ge k ge 4$ and sufficiently large $n$. We confirm their conjecture by proving a stronger statement. They also conjectured that for $m ge 4$ and sufficiently large $n$ the maximum size of a $3$-graph on $n$ vertices without a non-trivial intersecting subgraph of size $3m+1$ is achieved by certain Steiner systems. We give a construction with more edges showing that their conjecture is not true in general.
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