2000 cities each of which has exactly 3 roads to other cities
Source: Tuymaada 2000 Juniors 8
April 28, 2019
combinatoricsgraph theory
Problem Statement
There are cities in the country, each of which has exactly three roads to other cities. Prove that you can close roads, so that there is not a single closed route in the country, consisting of an odd number of roads.