A Helly-Type Theorem for Hyperplane Transversals to Well-Separated Convex Sets
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Let S be a finite collection of compact convex sets in \R d . Let D(S) be the largest diameter of any member of S . We say that the collection S is ɛ-separated if, for every 0 < k < d , any k of the sets can be separated from any other d-k of the sets by a hyperplane more than ɛ D(S)/2 away from all d of the sets. We prove that if S is an ɛ -separated collection of at least N(ɛ) compact convex sets in \R d and every 2d+2 members of S are met by a hyperplane, then there is a hyperplane meeting all the members of S . The number N(ɛ) depends both on the dimension d and on the separation parameter ɛ . This is the first Helly-type theorem known for hyperplane transversals to compact convex sets of arbitrary shape in dimension greater than one.