3 countries with cities connected with road
Source: Azerbaijan IZhO TST 2018 P4
August 1, 2023
combinatoricsTSTAZE IzHO TST
Problem Statement
There are cities in each of the three countries. Each road connects two cities from two different countries (there is at most one road between any two cities.) There are more than roads between these three countries. Prove that three cities, one city from each country, can be chosen such that there is a road between any two of these cities.