Mathematical clubs are popular among the inhabitants of the same city. Every two of them they have at least one member in common. Prove that we can give the people of the city compasses and rulers so that only one inhabitant gets both, while each club will to have both a ruler and a compass at the full participation of its members.
Problem
Source: Czech And Slovak Mathematical Olympiad, Round III, Category A 2016 p3
Tags: combinatorics