This application asks users to specify the size of a chess board and solves the corresponding N queens puzzle. The size of the board, i.e. the value of N, is bounded above by 8, although this limit can be easily altered.

A GUI is created when the program is executed. It has two buttons - one of them is for solving the puzzle to obtain the first solution, and the second button walks the users through all the remaining solutions.

Java is used to create the GUI and to run the application, while the N queens puzzle is solved by Prolog.

To run this program, you first need to install a Prolog engine. The one I currently use is SWI Prolog, which is available here. It is also necessary to add the home directory of Prolog to the PATH variable. Make sure that you can invoke 'swipl' on your command-line tool.

Next, assuming that you use Eclipse (Java IDE) for execution, create a new Java project containing all Java files and the Prolog script in this GitHub repository. Then add the JAR file jpl.jar to the build path of the Java project. This can be done by:

1. Right click on the project name in the package manager
2. Go to Build Path > Configure Build Path > Libraries
3. Click 'Add External JARs'
4. Select jpl.jar in the directory of Prolog. The JAR file usually resides in the lib folder.

If the program cannot be executed properly, reboot Eclipse and run the program again.

• The code in the Prolog script to solve the eight queens puzzle is attributed to The Art of Prolog by Ehud Shapiro and Leon Sterling.
• The image of a queen used in this application comes from this webpage.