MathDB
Problem 3

Source: 239-School Open Olympiad (Senior Level)

April 25, 2022
geometrycombinatorial geometryColorspoints

Problem Statement

Let AA be a countable set, some of its countable subsets are selected such that; the intersection of any two selected subsets has at most one element. Find the smallest kk for which one can ensure that we can color elements of AA with kk colors such that each selected subsets exactly contain one element of one of the colors and an infinite number of elements of each of the other colors.