<p>We show that for any large <i>n</i>, there exists a set of <i>n</i> points in the plane with <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(O(n^2/\sqrt{\log n})\)</EquationSource> </InlineEquation> distinct distances, such that any four points in the set determine at least five distinct distances. This answers (in the negative) a question of Erdős. The proof combines an analysis by Dumitrescu of forbidden four-point patterns with an algebraic construction of Thiele and Dumitrescu (to eliminate parallelograms), as well as a randomized transformation of that construction (to eliminate most other forbidden patterns).</p>

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Planar Point Sets with Forbidden 4-Point Patterns and Few Distinct Distances

  • Terence Tao

摘要

We show that for any large n, there exists a set of n points in the plane with \(O(n^2/\sqrt{\log n})\) distinct distances, such that any four points in the set determine at least five distinct distances. This answers (in the negative) a question of Erdős. The proof combines an analysis by Dumitrescu of forbidden four-point patterns with an algebraic construction of Thiele and Dumitrescu (to eliminate parallelograms), as well as a randomized transformation of that construction (to eliminate most other forbidden patterns).