rectangles in the coordinate plane
Source: Japan Mathematical Olympiad Finals, Problem 5
February 7, 2010
geometryrectangleanalytic geometrycombinatorics proposedcombinatorics
Problem Statement
Let be a set of 2002 points in the coordinate plane, no two of which have the same x\minus{} or y\minus{}coordinate. For any two points , consider the rectangle with one diagonal and the sides parallel to the axes. Denote by the number of points of lying in the interior of this rectangle. Determine the maximum such that, no matter how the points of are distributed, there always exist points in with .