Question 99
Some pairs of cities in a country are connected with one-directional direct flights (between any two cities, there is at most one flight).
We say that a city *A* is *accessible* for a city *B* if one may reach the city *A* starting at *B* (perhaps with zero flights or more than one flight in a chain). Assume that for any two cities *P* and *Q* there exists a city *R* for which each of *P* and *Q* is accessible. Prove that there exists a city for which every city is accessible. (V. Dolnikov)
We say that a city *A* is *accessible* for a city *B* if one may reach the city *A* starting at *B* (perhaps with zero flights or more than one flight in a chain). Assume that for any two cities *P* and *Q* there exists a city *R* for which each of *P* and *Q* is accessible. Prove that there exists a city for which every city is accessible. (V. Dolnikov)