Y by
In Tlaxcala, there is a transportation system that works through buses that travel from one city to another in one direction . A set
of cities is said beautiful if it contains at least three different cities and from each city
in
at least two buses depart, each one goes directly to a different city in
and none of them is
(if there is a direct bus from
to a city
in
, there is not necessarily a direct bus from
to
). Show that if there exists a beautiful set of cities
, then there exists a beautiful
subset of
, such that for any two cities in
, you can get from one to another by taking buses that only pass through cities in
.
Note: A bus goes directly from one city to another if it does not pass through any other city.















Note: A bus goes directly from one city to another if it does not pass through any other city.
This post has been edited 1 time. Last edited by parmenides51, Nov 13, 2021, 11:20 PM
Reason: typo: removed <em>
Reason: typo: removed <em>