The program: This program is used to determine if there are airline flights scheduled between a list of cities. Your program is required to do the following:

1. Determine if there is a path from the first city to the second, each identified by a three letter code.
2. Count the number of stops en-route (there may not be a direct flight.

FACTS:

The flights are listed in the following table:

List of Origin and Destination cities for direct flights

Origin City	Destination City
DGZ	QYY
DGZ	AZI
QYY	CSI
AZI	TVA
CSI	PPG
TVA	BRW
BRW	CSI

Use this information to form the facts of your program Remember, your rules are of the form:

myrelationship(city1, city2).

In this case the fact name might be something like: flight, from_to, direct_flight, or some other name that represents the concept represented.

RULES:

Your program will need a recursive rule similar to the rule for ancestor in the "Prolog Basics" link above. Here is a hint for counting the number of stops: If there is a direct flight, the number of stops is zero (basis case). If you have a route already, adding a new flight in the recursive part adds one to the number of stops.

Queries:

To test your program you should run the following queries:

• Find all the routes from DGZ to PPG (there should be two, one will have two stops, the other will have four stops)
• Find a route from TVA to CSI (there should be one stop)
• Find all the routes to BRW (there are 3).
• Find all the routes to PPG (there are 7 of them of with 0, 1, 2, 3, and 4 stops)

Sample output from these queries:

?- route(dgz, ppg, Stops). Stops = 2 ; Stops = 4 ; false. ?- route(tva,csi,Stops). Stops = 1 ; false. ?- route(Orig, brw, Stops). Orig = tva, Stops = 0 ; Orig = dgz, Stops = 2 ; Orig = azi, Stops = 1 ; false. ?- route(Orig,ppg, Stops). Orig = csi, Stops = 0 ; Orig = dgz, Stops = 2 ; Orig = dgz, Stops = 4 ; Orig = qyy, Stops = 1 ; Orig = azi, Stops = 3 ; Orig = tva, Stops = 2 ; Orig = brw, Stops = 1 ; false. ?- 

EXTRA Credit: You may receive 5 points extra credit for printing out the cities stopped in when there is no direct flight.

You can use SWI-Prolog to compile and run the code along with any other editing app. I was using sublime text. Thank you so much.