4 points of same color forming a rectangle in a 12x12 array, in 3 colours
Source: 1982 Swedish Mathematical Competition p5
March 28, 2021
Coloringcombinatorial geometrycombinatorics
Problem Statement
Each point in a array is colored red, white or blue. Show that it is always possible to find points of the same color forming a rectangle with sides parallel to the sides of the array.