Question 93
In a country, the government has decided to build a transport link between cities by railway or airline in such a way that no more than four other cities can be reached directly from each city. Prove that the government can always choose the type of connection of the corresponding pairs of cities in such a way that there are no three cities, each pair of which is connected by one type of transport.
(Arseniy Nicolaev)
Fig. 42
Fig. 43
(Arseniy Nicolaev)
Fig. 42
Fig. 43