Abstract.
A family of sets is Π n , or n -pierceable, if there exists a set of n points such that each member of the family contains at least one of them. It is Π k n if every subfamily of size k or less is Π n . Helly's theorem is one of the fundamental results in Combinatorial Geometry. It asserts, in the special case of finite families of convex sets in the plane, that Π 3 1 implies Π 1 . However, there is no k such that Π k 2 implies 2 -pierceability for all finite families of convex sets in the plane. It is therefore natural to propose the following:
Conjecture. There exists a k 0 such that, for all planar finite families of convex sets , Π k0 2 implies Π 3 .
Proofs of this conjecture for restricted families of convex sets are discussed.
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Received October 8, 1996, and in revised form August 12, 1997.
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Katchalski, M., Nashtir, D. A Helly Type Conjecture . Discrete Comput Geom 21, 37–43 (1999). https://doi.org/10.1007/PL00009408
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DOI: https://doi.org/10.1007/PL00009408