Respuesta :
The cities such that this path is [tex]C_{1}[/tex] → [tex]C_{2}[/tex] → [tex]C_{3}[/tex] . . . → [tex]C_{n}[/tex]. Now, if all roads are going towards [tex]c_{n}+1[/tex], then add  [tex]c_{n}+1[/tex] at the end of this path. Otherwise, let [tex]C_{i}[/tex] be the first city in this path such that there is a road from  [tex]C_{i}[/tex]-1 to  [tex]c_{n}+1[/tex] and from  [tex]c_{n}+1[/tex] to  [tex]C_{i}[/tex]. Place  [tex]c_{n}+1[/tex] between  [tex]C_{i}[/tex]−1 and  [tex]C_{i}[/tex] to get the desired path.
What is mathematical induction method?
Mathematical Induction is a technique of proving a statement, theorem or formula which is thought to be true, for each and every natural number n. By generalizing this in form of a principle which we would use to prove any mathematical statement is 'Principle of Mathematical Induction'.
The question says that between any two cities X and Y, either there’s an
one-way road from X to Y or from Y to X, but not both. Then show that
there is a path from some city A which visits all the cities exactly once.
This problem is very similar to the Football league problem #7 in Homework 1. This problem can be modeled as a directed graph in which cities
are represented as vertices and there’s an edge from vertices X to Y if
there’s a road from cities X to Y. And then, our goal is to find a path
in this graph which visits every vertex in the graph.
The rest of the solution is very similar to the argument in Problem 7 of
homework 1. We use induction of number of cities, say n.
As a base case, if n = 2, there are only two cities X and Y and the path
is simply the edge between X and Y.
For induction hypothesis, assume that the statement is true for any set
of n cities. That is’ for any set of n cities, we can find a path which visits
all the cities exactly once.
Let’s prove the statement for n + 1 cities. Leave out n + 1 th city (say,
[tex]c_{n}+1[/tex]) and for the remaining n cities, by induction hypothesis, we can find a path which visits all these n cities exactly once. Let us label the cities such that this path is [tex]C_{1}[/tex] → [tex]C_{2}[/tex] → [tex]C_{3}[/tex] . . . → [tex]C_{n}[/tex]. Now, if all roads are going towards [tex]c_{n}+1[/tex], then add  [tex]c_{n}+1[/tex] at the end of this path. Otherwise, let [tex]C_{i}[/tex] be the first city in this path such that there is a road from  [tex]C_{i}[/tex]-1 to  [tex]c_{n}+1[/tex] and from  [tex]c_{n}+1[/tex] to  [tex]C_{i}[/tex]. Place  [tex]c_{n}+1[/tex] between  [tex]C_{i}[/tex]−1 and  [tex]C_{i}[/tex] to get the desired path.
To learn more about induction hypothesis from the given link :
https://brainly.com/question/24672369
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