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Piercing convex sets

Noga Alon·Daniel J. Kleitman
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Abstract

A family of sets has the $(p,q)$ property if among any $p$ members of the family some $q$ have a nonempty intersection. It is shown that for every $p\ge q\ge d+1$ there is a $c=c(p,q,d)<\infty$ such that for every family $\scr F$ of compact, convex sets in $R^d$ that has the $(p,q)$ property there is a set of at most $c$ points in $R^d$ that intersects each member of $\scr F$. This extends Helly's Theorem and settles an old problem of Hadwiger and Debrunner.

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Noga Alon, Daniel J. Kleitman. 1992-10-01. Piercing convex sets. https://arxiv.org/abs/math/9210213

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