2020 points, black and green
Source: 2020 Austrian Federal Competition For Advanced Students, Part 2, p2
November 22, 2020
combinatoricsColoringpointsAustria
Problem Statement
In the plane there are points, some of which are black and the rest are green. For every black point, the following applies: There are exactly two green points that represent the distance from that black point.
Find the smallest possible number of green dots.(Walther Janous)